the star formation newsletterreipurth/newsletter/newsletter246.pdfafter my phd i took a trip to...

THE STAR FORMATION NEWSLETTERAn electronic publication dedicated to early stellar/planetary evolution and molecular clouds

No. 246 — 7 June 2013 Editor: Bo Reipurth ([email protected])

The Star Formation Newsletter

Editor: Bo [email protected]

Technical Editor: Eli [email protected]

Technical Assistant: Hsi-Wei [email protected]

Editorial Board

Joao AlvesAlan Boss

Jerome BouvierLee Hartmann

Thomas HenningPaul Ho

Jes JorgensenCharles J. Lada

Thijs KouwenhovenMichael R. MeyerRalph Pudritz

Luis Felipe RodŕıguezEwine van Dishoeck

Hans Zinnecker

The Star Formation Newsletter is a vehicle forfast distribution of information of interest for as-tronomers working on star and planet formationand molecular clouds. You can submit materialfor the following sections: Abstracts of recentlyaccepted papers (only for papers sent to refereedjournals), Abstracts of recently accepted major re-views (not standard conference contributions), Dis-sertation Abstracts (presenting abstracts of newPh.D dissertations), Meetings (announcing meet-ings broadly of interest to the star and planet for-mation and early solar system community), NewJobs (advertising jobs specifically aimed towardspersons within the areas of the Newsletter), andShort Announcements (where you can inform or re-quest information from the community). Addition-ally, the Newsletter brings short overview articleson objects of special interest, physical processes ortheoretical results, the early solar system, as wellas occasional interviews.

Newsletter Archivewww.ifa.hawaii.edu/users/reipurth/newsletter.htm

List of Contents

Interview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

My Favorite Object . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Perspective . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Abstracts of Newly Accepted Papers . . . . . . . . . . 14

Abstracts of Newly Accepted Major Reviews . 51

Dissertation Abstracts . . . . . . . . . . . . . . . . . . . . . . . . 53

Meetings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

Short Announcements . . . . . . . . . . . . . . . . . . . . . . . . 58

Cover Picture

NGC 7822 is an HII region, also known as Sharp-less 171, and located in Cepheus at the relativelyclose distance of 800 - 1000 pc. The central clusteris known as Berkeley 59. Parts of the complex areas young as 1-2 million years. The dominant ultra-violet source is the O5V star BD+66◦1673, whichis an eclipsing binary.

Image courtesy Martin Pugh.

Submitting your abstracts

Latex macros for submitting abstractsand dissertation abstracts (by e-mail [email protected]) are appended toeach Call for Abstracts. You can alsosubmit via the Newsletter web inter-face at http://www2.ifa.hawaii.edu/star-formation/index.cfm

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Hans Zinneckerin conversation with Bo Reipurth

Q: Hans, we have known each other for a long time, 30years, since the Les Houches school ”Birth and Infancy

of Stars”. How influential was that two week school in

August 1983 in the French Alps?

A: Very influential for many of us, myself included. Itwas there that long-term friendships among many youngastronomers were initiated. I vividly remember meet-ing John Bally, you Bo, Bruce Elmegreen, Gareth Wynn-Williams, Harold Yorke, to name but a few. Many of themfor the first time. This was the time when molecular out-flows were first discovered, as well as the proper motionsof Herbig-Haro objects, and I particularly recall discus-sions with George Herbig. It was also the time when thefirst results from the IRAS satellite began to appear, andduring the time of the school Bart Bok died in Tucson,AZ, making us feel that a baton was passed to the younggeneration.

Q: You presented your thesis work, a theoretical model ofthe log-normal IMF in Les Houches, didn’t you?

A: Yes indeed. I gave a presentation on star formation as arandom multiplicative process. The idea was that severalfactors determine the critical protostellar mass, such astemperature, density, magnetic flux, angular momentum,geometry, etc in a multiplicative fashion. By and largethis model is still valid (Fred Adams introduced outflowsin 1996) and Basu and Jones (2004) as well as Phil Myers(2011) realized how to turn the high-mass lognormal tailinto a (Salpeter) power-law slope by adding the idea thatthe accretion time is uniformly distributed. Perhaps myown contribution here was to realize that for a log-normalIMF that turns down below a certain characteristic mass,the predicted number of brown dwarfs (or black dwarfs asthese objects were then called) is small, i.e. the numbersdo not diverge towards small masses, as an extrapolatedSalpeter low-mass IMF would imply.

Q: Didn’t you also develop and coin the term ”competitiveaccretion” as a theoretical model for the IMF?

A: I guess this is correct. In my 1981 thesis I did two mod-els of the IMF, the log-normal model (originally based onthe concept of hierarchical fragmentation) and a power-law model (based on nonlinear Bondi-type gravitationalaccretion onto seed stars which were accreting from a lim-ited protocluster gas reservoir, hence the competition forgas accretion). This latter model was published in 1982 inthe Proc. of the Henry Draper Symposium on the OrionNebula and was popularized by Richard Larson who kindlyquoted my work. Had it not been for Richard, no-onemight have taken notice of that model. Now it is one ofmy most cited papers. Thank you, Richard.

Q: You were a theorist at heart, how come you turned intoa quasi-observational astronomer?

A: Yes, I started as a theorist, influenced by Prof. Kip-penhahn, and also by talking to Profs Bodenheimer andTscharnuter. Mind you, before my PhD in astrophysics Igot a diploma in physics in conformal quantum field the-ory - if anybody in astronomy knows what that is. Afterlooking around, I ended up for my thesis work in a group offar-infrared astronomers (balloon observations) at MPE inGarching, headed by Dr. Drapatz (my PhD thesis advisorwho taught me back-of-the envelope calculations). Thatenvironment helped me to get a sense for observations andthat the best astronomy is often done in interaction be-tween theory and observations.

Q: You did your postdoc years at the Royal ObservatoryEdinburgh. How did that happen?

A: Interesting story. Coincidences. After my PhD I took atrip to Hawaii and managed to force my way up to UKIRTon Mauna Kea (ask Eric Becklin about that particularfacet). At Hale Pohaku (the dormitory halfway up themountain, quite rudimentary in 1981) I happened to meetGerry Gilmore (then at ROE) and gave him a copy of mythesis (in German). Next thing I hear, after being backin Garching, was that Malcolm Longair (then director atROE) who was visiting ESO Garching for a colloquium,had asked my advisor to see him before his departure.Indeed I met with Malcolm and he offered me to come toROE as a postdoc, on the basis of a mixed Royal Societyand German Science Foundation fellowship. I stayed foralmost 4 years. This was a crucial move to turn me fromtheory to observations.

Q: Can you elaborate a little more?

A:. I try. At ROE, I met Tom Geballe with whom I didmy first observing proposal (Brackett alpha in the OrionNebula), Mark McCaughrean and John Rayner, both PhDstudents of Dr. Ian McLean, as well as Colin Aspin, MikeBurton, Ron Garden, and others. This reads like a who iswho in infrared arrays at the time (Ian McLean heading

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the IR-CAM development). I also there met Eric Becklin(on sabbatical) and Steve Beckwith (colloquium speaker),who alerted me to high angular resolution observations(lunar occultations and infrared speckle interferometry, re-spectively). Which I later applied to studies of pre-MainSequence binaries (originally with Chelli and Perrier 1986at ESO Chile and later with Leinert and Haas 1990 atCalar Alto). This exposure to infrared technology led to20 or so visits to Mauna Kea during my stay at ROE,which helped anchor my connection to observational as-tronomy.

Q: Apropos binaries. How did you get interested in pre-MS binaries?

A: When I arrived in Edinburgh in August 1983, I had justcome back from an IAU Colloquium on binarity and a totalsolar eclipse in Indonesia. I had to write a report for theGerman funding agency. This developed into a review onbinary statistics and star formation. Binary star formation(mass ratios) clearly was the next logical step, after deal-ing with the possible origin of stellar masses. Everythingin those days was kind of pristine territory in the youngfield of star formation. One could still read all the papersever written on the subject. As an aside, it may be worthmentioning that it took a discussion with a young womanfrom India (her name was Jitinder, a student at ROE) whoinsisted and convinced me to confront/test my fledglingtheories with detailed infrared observations. Why don’tyou? she asked, and so I succumbed and changed my re-search into a more observational direction. ROE was theperfect place for me to do this.

Q: I remember a visit to ROE which hosted the AustralianSchmidt telescope plate library in which I was interested.

On that visit the two of us had an important encounter.

Would you like to tell the story?

A: Well, I was working away, but you said why don’t youtake a break and come for a weekend walk in the High-lands. Eventually I gave in to your persuasion. We hikedto a place called Arrochar near Glasgow and Loch Lomondand kept walking until we finally reached the end of thetrack. There was a wooden bench waiting for us and in-scribed in it was the thoughtful phrase: REST and BETHANKFUL. Something to remember. We had a longtalk, and our ensuing (pre-internet) scientific interactionculminated in your invitation to spend three months asan ESO senior visitor at La Silla in 1991 to carry outour plan of a CCD visual binary survey among southernpre-Main Sequence stars with the NTT. We did it, andduring that time I also was able to start learning Spanish(at lunch). As you know I love languages, and learningSpanish had a big influence later in my life. When ourpaper was published in Nov 1993, two other independentbut similar pre-Main Sequence binary surveys were pub-lished in the very same month (Leinert et al. where I was

a co-author and Ghez et al.). This was a great month forme and in fact for young binary star research.

Q:: In 1994, you discovered the beautiful HH212 molecularhydrogen jet. How did this discovery come about?

A: Another interesting story which incidentally is con-nected to my deep interest in binary protostars. In 1987,in the early days of IR-arrays, I was interested in near-infrared imaging of cold, low-luminosity IRAS sources,in the hope to discover double stars in the same cloudcore, indicative of their joint formation (which was notyet proven at the time). IRAS 05413-0104 in Orion Bindeed showed two K-band near-infrared embedded pointsources, about 7 arcsec (300 AU) apart. Nothing hap-pened until 7 years later, when persistence paid off. Mycolleagues Mark McCaughrean and John Rayner (withme as a co-investigator) were observing the Orion Neb-ula Cluster with a new and better infrared array at theIRTF on Mauna Kea. Mark ran into a software problemrelated to the programming of the array mosaic patternand said: ”I need to fix this. You can have the telescopefor the next 10 min”. Well, intuition told me to have an-other look at that promising IRAS source with the near-infrared double star. So we changed target and took ashort integration. Upon inspecting the image, it seemedthe double star had become a quadruple system with allthe components aligned. Another deeper image resultedin an aligned system of 6 components. Wow. It was thenthat we realized that this could be a series of knots in amolecular hydrogen jet, as the H2 vibrational emission at2.12 micron fell into the K-band filter. We then switchedto the narrow-band 2.12 micron filter, and after a minuteor so, boom, the full highly bi-symmetric knotty jet inall its glory was revealed! By the way, the HH number(212) you gave the jet reflects the wavelength of its dis-covery. This serendipitous discovery was clearly my mostexciting observational experience (and perhaps my mostlasting legacy)!

Q:Which scientific question fascinates you most these days?

A: I would say: the formation of massive stars, in par-ticular the origin of the many close spectroscopic binarysystems among them. With orbital periods of a few days,separations of the order of 1 AU, and orbital speeds ofa few hundred km/s, these massive binaries challenge ourimagination. Some of these close binaries may even merge,to form very rapidly rotating single very massive O-stars.Maybe the progenitors of super-energetic long-durationgamma-ray bursts are related to massive binary star merg-ers or massive star collisions in dense clusters. In any case,the prevalence of these tight systems implies that binaryinteractions are the rule rather than the exception in mas-sive stellar evolution, something that many astrophysicistshave not fully realized.

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Q: Why did you decide to join the SOFIA Airborne Ob-

servatory?

A: I suppose I was looking for a new challenge. For 15years I was the head of the star formation group at AIPPotsdam and I think we had a good group of about tenoutstanding scientists and hence we had an unusally stim-ulating work environment. We were the coordinating nodeof the European Commission Research Training Networkon the Formation and Evolution of Young Stellar Clusters(2001-2004) and the founding partner of another EU Re-search Training Network ”Constellation” on the origin ofstellar masses (2006-2010). Mark McCaughrean was thedriving force and the interaction with him and his vast ob-servational and managerial experience provided an excit-ing framework and much fun for many years at AIP. RalfKlessen added the theoretical star formation and simula-tion component and thus our group had all the necessaryelements of strong interaction of theory and observations.When McCaughrean and Klessen moved on to higher po-sitions (ESA, ITA) I felt I was too old writing grant pro-posals to rebuild the group. Then the SOFIA opportunitycame along. Germany, with a 20 percent share in this bigbilateral project (80 percent US, i.e. NASA), was look-ing for a German representative and deputy director. Iapplied, not least because Eric Becklin (SOFIA chief sci-entist) overwhelmingly encouraged me to do so. I got thejob and 3 years ago moved to California, to NASA-Ameswhere the SOFIA science center is located.

Q: How are you doing at SOFIA?

A: Working at SOFIA has been a challenge from the be-ginning, not only because I had to learn so much aboutmanagement of science and mission operations, but alsobecause scientifically I had to switch from being mainly anear-infrared stellar astronomer to becoming a far-infraredinterstellar astronomer. What I like about SOFIA is thebroad wavelength coverage (from optical to far-infrared)with the potential of major discoveries over its projected20 year lifetime. SOFIA is working almost routinely now,and flying on SOFIA is a unique and cool experience. Ihave flown 4 times so far. After Herschel ran out of cryo-gen, SOFIA is the only far-infrared facility for many yearsto come. Ending my career with SOFIA, and consider-ing my small beginnings in the far-infrared group at MPEGarching in 1977, I feel I have come full circle, a verysatisfactory emotion some 35 years later.

Q: You have also worked extensively with X-ray data, right?

A: Yes, I turned from infrared to X-rays in 1990 becauseROSAT, the X-ray satellite built at MPE, was launchedand, working at MPE, it would have been foolish to ignoreit. My interest in X-rays soon brought me to the Univ. ofWürzburg in Germany (where X-rays were discovered in1895 by C.W. Röntgen). I enjoyed my time at the univer-sity working with bright young people there (notably Wolf-gang Brandner and Thomas Preibisch) and with my men-tor Harold Yorke, to whom I also owe much, as he saved mefrom ”extinction” when I was unable to get a permanentjob at age 40. Before leaving Würzburg for a permanentjob in Potsdam (at age 45), I initiated and co-organizedthe X-ray centenary conference ”Röntgenstrahlung fromthe Universe” in Würzburg in 1995. (My multi-lambdabackground, infrared and X-rays, earned me the job).

Q: That was just one of the several conferences and sym-

posia that you initiated. Which were the others?

A: Well, in Potsdam I launched the IAU Symposium ”TheFormation of Binary Stars”. I fought hard to get thememorable number IAUS 200 in the year 2000 for this bi-nary conference. Later, in 2004, I launched another majorconference in Tuscany/Italy ”50 years of the Initial MassFunction” in honor of Ed Salpeter who wrote his seminalIMF paper in 1954 (published in 1955). I am now plan-ning a first SOFIA science symposium in the Bay Area forthe summer of 2014 (just before the Brazil soccer worldcup for which I want to travel to Brazil. I love soccer, Iplayed myself in my younger years in Bavaria, and I lovethe Brazilian people).

Q:You have been to more conferences than any other as-

tronomer that I know, and you have a large collection of

photos from these meetings. Do you plan to make this

photo archive public?

A: Indeed I probably have the biggest set of private pic-tures of astronomers. My plan is to work on these andmake them available after I formally retire in 3.5 years.

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My Favorite ObjectIRAS 16293-2422

Luis Zapata

1 A Very Young Stellar Object

One of the consequences of the formation of a star isthe ”inside-out” collapse of dense parts of the molecu-lar clouds. This evolutionary phase is characterized bya central protostar and disk within an infalling envelopeof dust and gas. The infalling material passes through anaccretion disk, and then to the protostar allowing it togrow (Shu, Adams, and Lizano 1987). One of the veryfirst observational evidences of such infalling phenomenacame surprisingly from the young protostar IRAS16293-2422 (or L1689N) in the 80’s, almost in the same yearthat the famous Shu et al. review paper on star forma-tion was published. Figure 1 shows with a red box theposition of IRAS 16293 in the Rho Ophiuchi molecularcloud, one can see how this object is very embedded inits molecular natal cloud. The evidence for infall towardsIRAS16293 was based on a detailed analysis of the J=5-4 and 2-1 transitions of CS (Walker et al. 1986). Bothtransitions showed strong prominent self-absorption fea-tures superposed on a broader emission from an opticallythick molecular line. However, later Menten et al. (1987)using higher angular resolution CS J=3-2 and other linemaps argued that the kinematics of the CS gas might bebetter interpreted as rotation or outflow motions ratherthan infall. Recently, (sub)millimeter molecular line emis-sion maps obtained with ALMA have confirmed a directdetection of infall on the compact sources associated withIRAS16293. These studies for the first time have revealedstrong inverse P-Cygni profiles towards one source asso-ciated with IRAS16293 (Pineda et al 2012; Zapata et al.2013). In Figure 2 is shown the resolved infall motionstoward this component mapped at 690 GHz.

IRAS 16293 is an extremely cold far-infrared source lo-

Figure 1: Optical image of part of the Rho Ophiuchimolecular cloud and its vicinities. The yellowish star isAntares, and the M4 star cluster is to the right of Antares.The location of IRAS 16293-2422 is marked with a red box.This object is very embedded in its natal molecular cloudas one can be seen in this image. Image courtesy by TomO’Donoghue.

cated in the Rho Ophiuchi molecular cloud, one of theclosest places of recent star formation (located at a dis-tance of 120 pc; Loinard et al. 2008, Knude & Hog 1998).IRAS 16293 was first detected by the Infrared Astronomi-cal Satellite (IRAS) space-based observatory in the 25, 60,and 100 µm bands, this source is unresolved in all bands.The lack of detectable emission in the 12 µm band indi-cates that the source is a very cold dusty object.

Using the IRAS fluxes and a new data point at 2.7 mm ob-tained with the Owens Valley Radio Observatory (OVRO),Mundy et al. (1986) estimated a bolometric luminosityand a dust temperature of 27 L⊙ and 40 K for IRAS 16293,respectively. They confirmed that indeed this object isvery cold and is associated with a young low-mass proto-star. Such luminosity is in agreement with that value of23 L⊙ obtained by Walker et al. (1986), and the valueobtained recently by Correia et al. (2004) of 25 L⊙ (cor-rected with a more recent value of the distance).

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Figure 2: Upper: ALMA H13CN (blue), HC15N(magenta), and CH3OH (green) spectra from IRAS16293−2422B. The black dashed line marks the systemicLSR velocity of IRAS 16293−2422B (VLSR ∼ 3 km s

−1).

The observations made by Mundy et al. (1986) togetherwith subsequent high angular resolution observations (e.g.Wootten 1989) showed that IRAS16293 is really a binarysource separated by about 5′′. Moreover, the Very largeArray (VLA) centimeter observations fromWootten (1989)and Loinard et al. (2002) revealed that one component ofthe binary system, IRAS 16293A, splits up into a secondbinary system separated by only 50 AU. This binary sys-tem can be seen at resolutions better than about 0.2′′.These sources were named A1 and A2. The relative ori-entation of the A1/A2 pair at the time of its discoverywas very similar to the direction of the NE-SW flow, andA1 was initially believed to be an ejecta from A2. How-ever, analysis of the relative motion of A1 and A2 favorsa scenario where these two sources trace two stars in a bi-nary system (Loinard 2002; Chandler et al. 2005; Loinardet al. 2007; Pech et al. 2010). The other componentB remains single even at the highest angular resolutionavailable (∼ 0.05′′; Chandler et al. 2005; Rodŕıguez etal. 2005). Subarcsecond submillimeter continuum ob-servations obtained with the Submillimeter Array (SMA)revealed additional structure in component A called Ab(Chandler et al. 2005). This source has not been detectedat any other wavelengths so far, and its exact nature re-mains poorly understood.

Mundy et al. (1992) suggested that the southeastern sourceIRAS 16293A contains only ∼ 0.5 M⊙ of dust and gas in a

Figure 3: SMA integrated blueshifted (blue contours) andredshifted (red contours) CO J=2-1 map of the outflowsfrom IRAS 16293-2422. Image taken from Yeh et al.(2008). The black circles represent the FWHM of theSMA. The crosses denote the positions of the two con-tinuum sources. Positions of the two prominent compactcomponents are labeled (b1 and b2). The filled ellipseindicates the synthesized beam size.

region of about 4′′ and its associated centimeter emissionis most likely produced by an ionized stellar wind as dis-cussed by Wootten (1989). On the other hand, the north-western source IRAS 16293B, displays continuum emissionwhich increases as ν2 throughout millimeter and centime-ter wavelengths (Estalella et al. 1991). This unique spec-trum can be explained if most of the continuum emissionis arising from dust. Subsequent observations made byRodŕıguez et al. (2005) and Chandler et al. (2005) showthat IRAS 16293B has a spectral energy index of ν2.0−2.6

and a size of only 25 AU.

2 Outflows

Among the first works to detect outflows associated withIRAS 16293-2422 were those of Wootten et al. (1987) andMizuno et al. (1990). The multiple CO observations fromthese two studies revealed that the high velocity gas is re-solved into four compact separate lobes, consisting of twopairs of bipolar lobes, in addition to an extended monopo-lar blueshifted lobe. The quadrupolar outflow associatedto this source is oriented with one bipolar flow almosteast(blueshifted)-west(redshifted) (at a position angle of∼ 55◦), and the second one with its axis with an orienta-

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Figure 4: Comparison between five radio images of IRAS16293A at different epochs. Note how the morphology ofcomponent A2 changes with time, while the other (A1)remains the same. Image taken from Pech et al. (2008).

tion northeast(redshifted)-southwest(blueshifted) or at aposition angle ∼ 110◦. Both flows seem to emanate fromIRAS 16293-2422A and B. A SMA map of compact COemission obtained by Yeh et al. (2008) is presented in Fig-ure 3. In this Figure one can clearly see the multiple east-west outflows emanating from this complex region. Someof these CO lobes coincide very well with SiO emission,a typical outflow tracer (Hirano et al. 2001). To explainthe conspicuous quadrupolar morphology of this outflowsystem, Walker et al. (1993) proposed that the two pairsof lobes correspond to two independent bipolar outflowsdriven by two independent sources. On the other hand,Mizuno et al. (1990) showed that the outflow is dynam-ically interacting with the dense ambient gas clump andsuggested that a single outflow lobe could be split into twolobes by the interaction. More recent observations fromStark et al. (2004) proposed that the northeast-southwestflow is powered by I16293A, while the east-west fossil flow

Figure 5: ALMA Integrated intensity of the weighted ve-locity (moment 1) colour map of the CO(6-5) emissionfrom source B overlaid in contours with the 0.45 mm con-tinuum emission (black thick line) and the velocity scaleof CO(6-5) (grey thin line). Image taken from Loinard etal. (2012).

was ejected from I16293B long time ago. In addition, theymentioned that maybe I16293B is a not so young star, per-haps a T-Tauri star because of its fossil outflow. However,Laurent et al. (2013) using ALMA observations proposedthat this east-west fossil outflow could also arise from thevicinities of I16293A. These ALMA observations revealeda very compact east-west bipolar outflow emanating fromthis object that maybe is the base of the large-scale out-flow.

Monitoring of IRAS 16293-2422 at centimeter wavelengthswith the VLA and now with the recently finished JVLA(Jansky Very Large Array) has allowed to detect an episodicand compact northeast-southwest ionized flow associatedwith the source IRAS 16293 A2 (Loinard et al. 2007; Pechet al. 2010), see Figure 4. This ionized flow has a a pro-jected velocity of 30-80 km s−1, and with the mass of eachejecta of the order of 10−8 M⊙. Pech et al. (2010) pro-posed that this ionized episodic outflow could energize atlarge scales the northeast-southwest molecular outflow re-ported by Wootten et al. (1989) and Mizuno et al. (1990).

Recently, 690 GHz submillimeter observations with ALMA(The Atacama Large Millimeter Array) revealed that thesource IRAS 16293 B is driving a southeast compact out-flow (Loinard et al. 2013). However, the flow has peculiarproperties: it is highly asymmetric, bubble-like, fairly slow(10 km s−1), and lacking of a jet-like feature along its sym-

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Figure 6: ALMA Spectra in the central beams towardthe continuum peaks of IRAS 16293A (upper) and IRAS16293B (lower). In both panels is shown the detection ofthe Glycolaldehyde (HCOCH2OH) molecule. Image takenfrom Jørgensen et al. (2012).

metry axis. In addition, its dynamical age is only about200 years. In Figure 5 is shown this bubble-like outflowas revealed by the ALMA observations. However, usingthe same set of data, Kristensen et al. (2012), proposedthat this submillimeter CO emission is not associated withIRAS 16293 B, instead, a blue-shifted bow shock fromsource A is overlapping with source B in the plane of thesky. Outflow entrainment takes place over large scales, >100 AU, and wind material is decelerated through directinteraction with the envelope.

3 Molecules and Chemistry

IRAS 16293-2422 has long been considered one of the”template” sources for astrochemistry as mentioned byJørgensen et al. (2012). It has been the subject of many(sub)millimeter spectroscopic studies using single dishesand interferometers (Blake et al. 1994; van Dishoeck etal. 1995; Ceccarelli et al. 1998; Cazaux et al. 2003;Chandler et al. 2005; Caux et al. 2011; Jørgensen etal. 2011) as well as specialized modeling efforts tryingto establish its chemical composition. Particularly, thevariation in its molecular abundances as function of ra-dius has been studied (e.g., Schöier et al. 2002). Thedetections of complex molecules toward this source (e.g.,Cazaux et al. 2003; Bottinelli et al. 2004; Kuan et al.2004; Bisschop et al. 2008; Jørgensen et al. 2012) haveopened new interest in the physical processes that can leadto the evaporation of icy grain mantles. Figure 6 showsthe ALMA spectrum where the complex molecule Glyco-laldehyde (HCOCH2OH) is detected. It has also been the

target of many studies trying to relate the structure ofthe two main components to their line emission and placethem in an evolutionary scheme. As mentioned earlier thesoutheastern of the two components, IRAS 16293A, ap-pears resolved in continuum observations, breaking intoa number of different components at subarcsecond scales(Chandler et al. 2005; Pech et al. 2010). The northwest-ern component, IRAS 16293B, in contrast appears unre-solved on these scales. In terms of line emission the twosources also show significant differences: both show detec-tion of complex organic molecules (see for example: Bot-tinelli et al. 2004; Kuan et al. 2004; Remijan & Hollis2006; Bisschop et al. 2008), but the relative line strengthsand widths vary between the two sources, see Figure 6.

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9

Perspective

Feedback Processesby James E. Dale

The ability of infra–red and submillimetre space missionssuch as Spitzer, WISE and Herschel to see deep insidestar–forming regions has brought extraordinary advancesin our understanding of starbirth. One of the fields thathas benefitted most from this avalanche of new data isthe study of the effects of stellar feedback processes onmolecular clouds.

On scales of ∼1 up to ∼ 100 pc, the structure of thecold interstellar medium (ISM) is dominated by hot bub-bles and swept–up shells of dense, cooler material (e.g.Churchwell et al. 2006, 2007, Deharveng et al. 2010).Figure 1 shows a striking example from the WISE mission(Koenig et al., 2012). Where expanding bubbles are ableto break out of their host clouds, champagne flows result.On smaller scales on the edges of bubbles or inside them,we see pillars, cometary knots and proplyds (e.g. Smith etal. 2004, Billot et al. 2010). It is clear that the structureand appearance of most star–forming regions is governedby the action of feedback from their own stars.

What is much less clear from these observations is theeffect of feedback on the dynamical state of the cloudsand their embedded clusters, and on the star formationprocess itself on cloud scales.

A simple model of star formation in molecular clouds basedpurely on gravitational contraction and collapse results instar formation rates much higher than are observed ongalactic scales (Zuckerman & Evans, 1974). Among thesolutions proposed to this problem is the suggestion thatfeedback processes decrease the star formation efficiency

by expelling gas from clouds before it is able to collapseor be accreted (e.g. Whitworth, 1979).

Observations (e.g. Evans et al 2009) confirm that typicalstar formation efficiencies on the size–scales of molecularclouds are never more than ten percent in the Milky Way.While these efficiencies are not low enough to account forthe very slow Galactic star formation rate, they neverthe-less invite explanation.

Low star formation rates on GMC scales have a corollarythat may provide insight into another long–standing is-sue, namely the dissolution of the vast majority of stellarclusters while still very young (Lada & Lada 2003). If gasexpulsion occurs early enough and fast enough, the poten-tial well of the forming embedded cluster can in principlebecome too shallow to retain its stars (Hills 1980).

GMCs are turbulent and highly substructured, so that,even in the absence of feedback, their evolution is so com-plex that it must be modelled numerically. Increasingcomputer power and new algorithms have recently madethe inclusion of stellar feedback in such simulations possi-ble (e.g Offner et al. 2009, Krumholz et al. 2010, Walchet al 2012).

Recently Dale et al (2012a,b, 2013a,b) performed a setof smoothed–particle hydrodynamics (SPH) simulations ofthe influence of expanding HII regions on a mass–radiusparameter space of turbulent clouds. We chose the pa-rameter space to cover the observed properties of GMCsreported by Heyer et al (2009), although neglecting lowermass (∼ 103 M⊙) clouds, since they are unlikely to formany massive stars. This resulted in a set of clouds with

Figure 1: Infrared image of W3/4/5 from the WISE space-craft (Koenig et al. 2012). The width of the region shownis approximately 200pc and the bubble diameters are ap-proximately 50pc. Credit: NASA, JPL-Caltech, WISETeam.

10

Mcloud ∈ [104, 106] M⊙, Rcloud ∈ [2.5, 180] pc. Clouds were

seeded with turbulent velocity fields so that the initial ra-tios of kinetic to gravitational potential energy were either0.7 or 2.3, giving a set of bound and unbound clouds.

The clouds were allowed to evolve and form stars. They allexhibit complex structure generated by the imposed tur-bulent velocity fields. The gas forms a network of densefilaments along which gas tends to flow towards the clouds’centres of mass. This leads to the formation of stellar clus-ters at filament junctions, as has been observed by, e.g.,Schneider et al. (2012). In some cases, the filaments aredense enough to fragment along their lengths, resulting inlinear groupings of stars. However, these stars tend to fol-low the gas flow along the filaments into the nearest clusteron relatively short timescales. An example of a 105 M⊙globally unbound cloud is shown in Figure 2.Colours rep-resent gas column densities projected along the z–axis.White dots are SPH sink particles which, in this case,represent small clusters rather than individual stars. Thefilamentary structure of the gas and the association of starformation with the filaments are clearly visible.

10−4 10−3 10−2 10−1 100

log Σ (g cm−2)

−75

−50

−25

0

25

50

75

y(p

c)

−75 −50 −25 0 25 50 75

x (pc)

Figure 2: Column density map of the 105 M⊙ globallyunbound Run UV cloud from Dale et al (2012b) beforethe onset of feedback. White dots represent star clusters.

Accretion flows inevitably result in a few stars growing tobe O–stars (in the simulations where individual stars couldbe resolved), or a few clusters growing massive enough tohost O–stars (otherwise). These objects were then given

ionizing photon fluxes appropriate to their masses and theclouds were evolved for a further 3 Myr, the approximateinterval between the formation of the first O–stars andtheir explosions as supernovae. The effects of the resultingHII regions on the clouds depends strongly on the struc-ture and properties of the clouds themselves. The massivestars and clusters are born inside the densest gas and thismaterial initially restricts the rate at which they can ionizethe gas by collimating their radiation fields. The O–starsare thus typically able to ionize only a few to ten percentof their host clouds’ total masses.

The temperature inside HII regions is fixed by an equilib-rium between heating and cooling process (Osterbrock &Ferland 2006), so that the sound speed in the ionized gashas a constant value of ≈ 10 km s−1. This is dynamicallyimportant because it sets an upper limit on the velocityto which expanding HII regions can accelerate surroundingmaterial. The ability of the HII regions to disrupt cloudsdepends on the clouds’ escape velocities. Since

vESC ∼ (Mcloud/Rcloud)1

2 ,

and the model clouds follow the observed trend of havingconstant column density, so that

Mcloud ∼ R2cloud,

it follows that

vESC ∼ (Mcloud)1

4 .

The escape velocity is then a slowly–growing function ofcloud mass. The masses of clouds in the chosen parameterspace range over two orders of magnitude, so that theescape velocity varies by a factor of a few from a few kms−1 to in excess of 10 km s−1. This relatively small rangein one particular property is the main determinant in thereaction of the clouds to their HII regions.

In lower–mass, low–vESC clouds, the HII regions destroythe filamentary gas and expand into much of the cloud vol-ume, creating ∼10pc–scale bubbles and sweeping up shellsof dense material, as shown in Figure 3. In these cases,the resulting systems bear a striking resemblance to ob-jects like W3/4/5, shown in Figure 1. In more massiveclouds, however, photoionization is unable to disrupt thefilaments and ionized gas leaks into pre–existing voids gen-erated by the imposed turbulent velocity fields. In bothcases, the permeability of the gas distribution allows largequantities of ionized gas to escape the clouds entirely. Thislowers the pressure in the HII regions and further limitsthe damage done to the clouds by feedback. These resultssuggest that other means of disrupting ∼ 106 M⊙ cloudsneed to be found.

11

10−4 10−3 10−2 10−1 100

log Σ (g cm−2)

−75

−50

−25

0

25

50

75

y(p

c)

−75 −50 −25 0 25 50 75

x (pc)

Figure 3: Column density map of the same 105 M⊙ glob-ally unbound Run UV cloud from Dale et al (2012b) after3 Myr of photoionization. White dots represent star clus-ters.

Although feedback is usually suggested as a means of lim-iting the star–forming capacity of clouds, there has alsobeen a great deal of interest in the idea that it may alsotrigger star formation (Elmegreen & Lada 1977). Thisimmediately raises the question of what is the net effectof feedback on the star–formation efficiency. This is verydifficult to answer objectively from an observational per-spective, since it requires the evaluation of a counterfac-tual argument – that of how a given system would haveevolved in the absence of feedback.

The same problem is relatively easy to approach numeri-cally, however, simply by repeating simulations with feed-back effects switched off. If this is done using a Lagrangianhydrodynamics scheme such as SPH, it allows one to de-termine not only how the star formation efficiency is al-tered by feedback, but which stars have been induced toform, prevented from forming or simply caused to formsomewhere else.

In Dale et al. (2013b), we showed that all of these pro-cesses – triggered star formation, aborted star formation,and redistribution of spontaneously–formed stars – oper-ate locally. Ionizing feedback can thus cause the geometryof star formation in a given cloud to be radically differ-ent. However, it was found that such feedback always

reduced the overall star formation efficiencies. The de-structive effects of the massive stars/clusters on the densefilaments where most star formation was taking place out-weighed any triggering taking place in outlying regions ofthe clouds.

It was also observed that the triggered objects tended to bespatially mixed with spontaneously–formed objects. Thiswas a consequence of expanding bubbles sweeping up andcompressing both gas that was going to form stars any-way, and quiescent material that would otherwise be sta-ble, and transporting it to the same locations. Thus, thegeometrical association of a given star with the edge of abubble, an ionization front, or even a pillar structure, isnot a foolproof indicator that the star has been inducedto form. This is illustrated in Figure 4 where a greyscalecolumn–density map from the Run I simulation from Daleet al. (2013b) is shown. Stars are overlaid as circles forspontaneously–formed objects and triangles for triggeredobjects, all colour–coded by mass. Note that the threeobjects near the tip of the prominent pillar in the bottomleft of the frame are not triggered.

−15 −10 −5 0 5 10 15x(pc)

−15

−10

−5

0

5

10

15

y(p

c)

−0.25

0.00

0.25

0.50

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1.00

1.25

1.50

1.75

Log

(ste

llar

mass

) (M

⊙)Figure 4: Column density map (greyscale) of the 104 M⊙Run I cloud from Dale et al (2013b) after 3 Myr of pho-toionization. Circles represent spontaneously–formed ob-jects and triangles denote triggered objects, all colour–coded by mass.

In reality, photoionization and winds from massive starsact simultaneously. Capriotti & Kozminski (2001) com-pared the separate influence of expanding HII regions andwinds on uniform clouds and concluded that HII regionswere likely to be more important except in very dense gas(n> 106 cm−3). McKee et al (1984), McCray & Kafatos(1987), Matzner (2002) and Fryer et al (2003, 2006) allargue that wind bubbles are likely to be trapped insideHII regions, except for the case of very massive stars or

12

very bright clusters.

These studies all rely on semi–analytic treatments or theuse of smooth initial geometries. It is not clear what thecombined effects of these two forms of feedback will beon complex turbulent clouds. It is possible that the windswould help the massive stars disrupt the dense filamentarygas in which they are born and thus reduce the collimatingeffect of this material on their radiation fields.

Once the combined outcome of ionization and winds hasbeen established, the environment in which the first su-pernovae will explode is determined. This is of crucialimportance in understanding the appearance and evolu-tion of supernova remnants. The feedback–sculpted cloudstructure will also determine what fraction of the heavyelement–polluted debris is ejected from the clouds directly,or stopped locally and immediately involved in a secondround of star formation. This latter issue has strong impli-cations for the existence of multiple generations of stars(distinguished by their metallicity) in the same clusters(e.g. Marino 2009).

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13

Abstracts of recently accepted papers

A Near-Infrared Spectroscopic Study of Young Field Ultracool Dwarfs

K. N. Allers1 and Michael C. Liu2

1 Department of Physics and Astronomy, Bucknell University, Lewisburg, PA 17837, USA2 Institute for Astronomy, University of Hawai’i, 2680 Woodlawn Drive, Honolulu, HI 96822, USA

E-mail contact: k.allers at bucknell.edu

We present a near-infrared (0.9–2.4 µm) spectroscopic study of 73 field ultracool dwarfs having spectroscopic and/orkinematic evidence of youth (≈10–300 Myr). Our sample is composed of 48 low-resolution (R≈100) spectra and41 moderate-resolution spectra (R≈750-2000). First, we establish a method for spectral typing M5–L7 dwarfs at near-IR wavelengths that is independent of gravity. We find that both visual and index-based classification in the near-IRprovide consistent spectral types with optical spectral types, though with a small systematic offset in the case of visualclassification at J and K band. Second, we examine features in the spectra of ∼10 Myr ultracool dwarfs to define a setof gravity-sensitive indices based on FeH, VO, K, Na, and H-band continuum shape. We then create an index-basedmethod for classifying the gravities of M6–L5 dwarfs that provides consistent results with gravity classifications fromoptical spectroscopy. Our index-based classification can distinguish between young and dusty objects. Guided by theresulting classifications, we propose a set of low-gravity spectral standards for the near-IR. Finally, we estimate theages corresponding to our gravity classifications.

Accepted by ApJ

http://arxiv.org/pdf/1305.4418

The Mass Dependence Between Protoplanetary Disks and their Stellar Hosts

Sean M. Andrews1, Katherine A. Rosenfeld1, Adam L. Kraus1 and David J. Wilner1

1 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA

E-mail contact: sandrews at gmail.com

We present a substantial extension of the millimeter-wave continuum photometry catalog for circumstellar dust disksin the Taurus star-forming region, based on a new ”snapshot” λ = 1.3mm survey with the Submillimeter Array.Combining these new data with measurements in the literature, we construct a mm-wave luminosity distribution,f(Lmm), for Class II disks that is statistically complete for stellar hosts with spectral types earlier than M8.5 andhas a 3-σ depth of roughly 3mJy. The resulting census eliminates a longstanding selection bias against disks withlate-type hosts, and thereby demonstrates that there is a strong correlation between Lmm and the host spectral type.By translating the locations of individual stars in the Hertzsprung-Russell diagram into masses and ages, and adoptinga simple conversion between Lmm and the disk mass, Md, we confirm that this correlation corresponds to a statisticallyrobust relationship between the masses of dust disks and the stars that host them. A Bayesian regression technique isused to characterize these relationships in the presence of measurement errors, data censoring, and significant intrinsicscatter: the best-fit results indicate a typical 1.3mm flux density of ∼25mJy for 1M⊙ hosts and a power-law scalingLmm ∝ M

1.5−2.0∗ . We suggest that a reasonable treatment of dust temperature in the conversion from Lmm to Md

favors an inherently linear Md ∝ M∗ scaling, with a typical disk-to-star mass ratio of ∼0.2–0.6%. The measured RMSdispersion around this regression curve is ±0.7 dex, suggesting that the combined effects of diverse evolutionary states,dust opacities, and temperatures in these disks imprint a FWHM range of a factor of ∼40 on the inferred Md (or Lmm)at any given host mass. We argue that this relationship between Md and M∗ likely represents the origin of the inferredcorrelation between giant planet frequency and host star mass in the exoplanet population, and provides some basicsupport for the core accretion model for planet formation. Moreover, we caution that the effects of incompletenessand selection bias must be considered in comparative studies of disk evolution, and illustrate that fact with statisticalcomparisons of f(Lmm) between the Taurus catalog presented here and incomplete subsamples in the Ophiuchus, IC

14


348, and Upper Sco young clusters.

Accepted by Astrophysical Journal


Asymmetric transition disks: Vorticity or eccentricity?

S. Ataiee1,2, P. Pinilla1, A. Zsom3, C.P. Dullemond1, C. Dominik4,5 and J. Ghanbari2

1 Heidelberg University, Center for Astronomy, Institute for Theoretical Astrophysics, Albert Ueberle Str. 2, 69120Heidelberg, Germany2 Department of Physics, Faculty of Sciences, Ferdowsi University of Mashhad, Mashhad, Iran3 Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA02139, USA4 Anton Pannekoek Institute for Astronomy, University of Amsterdam, Postbus 94249, 1090 GE Amsterdam, theNetherlands5 Afdeling Sterrenkunde, Radboud Universiteit Nijmegen, Postbus 9010, 6500 GL, Nijmegen, the Netherlands

E-mail contact: sareh.ataiee at gmail.com

Transition disks typically appear in resolved millimeter observations as giant dust rings surrounding their young hoststars. More accurate observations with ALMA have shown several of these rings to be in fact asymmetric: theyhave lopsided shapes. It has been speculated that these rings act as dust traps, which would make them importantlaboratories for studying planet formation. It has been shown that an elongated giant vortex produced in a disk witha strong viscosity jump strikingly resembles the observed asymmetric rings. We aim to study a similar behavior fora disk in which a giant planet is embedded. However, a giant planet can induce two kinds of asymmetries: (1) agiant vortex, and (2) an eccentric disk. We studied under which conditions each of these can appear, and how one canobservationally distinguish between them. This is important because only a vortex can trap particles both radially andazimuthally, while the eccentric ring can only trap particles in radial direction. We used the FARGO code to conductthe hydro-simulations. We set up a disk with an embedded giant planet and took a radial grid spanning from 0.1 to7 times the planet semi-major axis. We ran the simulations with various viscosity values and planet masses for 1000planet orbits to allow a fully developed vortex or disk eccentricity. Afterwards, we compared the dust distributionin a vortex-holding disk with an eccentric disk using dust simulations. We find that vorticity and eccentricity aredistinguishable by looking at the azimuthal contrast of the dust density. While vortices, as particle traps, producevery pronounced azimuthal asymmetries, eccentric features are not able to accumulate millimeter dust particles inazimuthal direction, and therefore the asymmetries are expected to be modest.

Accepted by Astronomy & Astrophysics


Enhanced Hα

activity at periastron in the young and massive spectroscopic binaryHD200775

M. Benisty1,2, K. Perraut1, D. Mourard3, P. Stee3, G. Lima1, J.B. LeBouquin1, M. Borges Fernandes4,

O. Chesneau3, N. Nardetto3, I. Tallon-Bosc5, H. McAlister6,7, T. Ten Brummelaar7, S. Ridgway8, J.

Sturmann7, L. Sturmann7, N. Turner7, C. Farrington7 and P.J. Goldfinger7

1 IPAG, Grenoble, France2 MPIA, Heidelberg, Germany3 OCA, Nice, France4 Observatorio Nacional, Rio de Janeiro, Brazil5 Universite de Lyon, France6 Georgia State University, USA7 CHARA Array, USA8 NOAO, Tucson, USA

E-mail contact: Myriam.Benisty at obs.ujf-grenoble.fr

[A&A abstract abridged] Young close binaries clear central cavities in their surrounding circumbinary disk from which

15

http://arxiv.org/pdf/1305.5262http://arxiv.org/pdf/1304.1736

the stars can still accrete material. This process takes place within the very first astronomical units, and is still notwell constrained as the observational evidence has been gathered, until now, only by means of spectroscopy. Duringa full orbital period (∼3.6 yrs) we observed the young massive spectroscopic binary HD200775 (separation ∼5 AU)with the VEGA instrument on the CHARA array and spatially and spectrally resolved its Hα emission, at low andmedium spectral resolutions (R∼1600 and 5000). Combining the radial velocity measurements and astrometric dataavailable in the literature, we determined new orbital parameters. We observe that the Hα equivalent width varieswith the orbital phase, and increases close to periastron, as expected from theoretical models that predict an increaseof the mass transfer from the circumbinary disk to the primary disk. In addition, we have found marginal variationsof the typical extent of the Hα emission (at 1 to 2σ level) and location (at 1 to 5σ level). The spatial extent of theHα emission, as probed by a Gaussian FWHM, is minimum at the ascending node (0.22±0.06 AU), and more thandoubles at periastron. In addition, the Gaussian photocenter is slightly displaced in the direction opposite to thesecondary, ruling out the scenario in which all or most of the emission is due to accretion onto the secondary. Thesefindings, together with the wide Hα line profile, favor a scenario in which the enhanced Hα activity at periastron maybe due to a non-spherical wind around the primary and enhanced at periastron.

Accepted by Astronomy & Astrophysics


Detection of 15NNH+ in L1544: non-LTE modelling of dyazenilium hyperfine line emis-sion and accurate 14N/15N values

Luca Bizzocchi1, Paola Caselli2, Elvira Leonardo1 and Luca Dore3

1 CAAUL, Observatório Astronómico de Lisboa, Tapada da Ajuda, 1349-018 Lisboa, Portugal2 School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, UK3 Dipartimento di Chimica ”G. Ciamician”, Universita di Bologna, via F. Selmi 2, 40126 Bologna, Italy

E-mail contact: bizzocchi at oal.ul.pt

Samples of pristine Solar System material found in meteorites and interplanetary dust particles are highly enriched in15N. Conspicuous nitrogen isotopic anomalies have also been measured in comets, and the 14N/15N abundance ratio ofthe Earth is itself larger than the recognised pre-solar value by almost a factor of two. Ion–molecules, low-temperaturechemical reactions in the proto-solar nebula have been repeatedly indicated as responsible for these 15N-enhancements.We have searched for 15N variants of the N2H

+ ion in L1544, a prototypical starless cloud core which is one of thebest candidate sources for detection owing to its low central core temperature and high CO depletion. The goal isthe evaluation of accurate and reliable 14N/15N ratio values for this species in the interstellar gas. A deep integrationof the 15NNH+ (1-0) line at 90.4GHz has been obtained with the IRAM 30m telescope. Non-LTE radiative transfermodelling has been performed on the J = 1− 0 emissions of the parent and 15N-containing dyazenilium ions, using aBonnor–Ebert sphere as a model for the source. A high-quality fit of the N2H

+ (1–0) hyperfine spectrum has allowedus to derive a revised value of the N2H

+ column density in L1544, and the analysis of the observed N15NH+ and15NNH+ spectra yielded an abundance ratio N(N15NH+)/N(15NNH+) = 1.1 ± 0.3. The obtained 14N/15N isotopicratio is ∼ 1000± 200, suggestive of a sizeable 15N depletion in this molecular ion. Such a result is not consistent withthe prediction of present nitrogen chemical models: as they predict large 15N fractionation of N2H

+, we suggest that15N14N, or 15N in some other molecular form, is preferentially depleted onto dust grains.

Accepted by Astronomy and Astrophysics


Deuterium Burning in Massive Giant Planets and Low-Mass Brown Dwarfs formed byCore-Nucleated Accretion

Peter Bodenheimer1, Gennaro D’Angelo2,4,5, Jack J. Lissauer2, Jonathan J. Fortney1, and Didier

Saumon3

1 UCO/Lick Observatory, Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA95064, USA2 Space Science and Astrobiology Division, NASA Ames Research Center, Moett Field, CA 94035, USA

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3 Los Alamos National Laboratory, P. O. Box 1663, Los Alamos, NM 87545, USA4 SETI Institute, 189 Bernardo Avenue, Mountain View, CA 94043, USA5 Visiting Research Scientist, Los Alamos National Laboratory, Los Alamos, NM 87545, USA

E-mail contact: peter at ucolick.org

Formation of bodies near the deuterium-burning limit is considered by detailed numerical simulations according tothe core-nucleated giant planet accretion scenario. The objects, with heavy-element cores in the range 5–30 M⊕, areassumed to accrete gas up to final masses of 10–15 Jupiter masses (Mjup). After the formation process, which lasts1–5 Myr and which ends with a ’cold-start’, low-entropy configuration, the bodies evolve at constant mass up to anage of several Gyr. Deuterium burning via proton capture is included in the calculation, and we determined the mass,M50, above which more than 50% of the initial deuterium is burned. This often-quoted borderline between giantplanets and brown dwarfs is found to depend only slightly on parameters, such as core mass, stellar mass, formationlocation, solid surface density in the protoplanetary disk, disk viscosity, and dust opacity. The values for M50 fallin the range 11.6–13.6 Mjup, in agreement with previous determinations that do not take the formation process intoaccount. For a given opacity law during the formation process, objects with higher core masses form more quickly. Theresult is higher entropy in the envelope at the completion of accretion, yielding lower values of M50. For masses aboveM50, during the deuterium-burning phase, objects expand and increase in luminosity by 1 to 3 orders of magnitude.Evolutionary tracks in the luminosity-versus-time diagram are compared with the observed position of the companionto Beta Pictoris.

Accepted by ApJ


OH (1720 MHz) Masers: A Multiwavelength Study of the Interaction between theW51C Supernova Remnant and the W51B Star Forming Region

C.L. Brogan1, W.M. Goss2, T.R. Hunter1, A.M.S. Richards3, C.J. Chandler2, J.S. Lazendic4, B.-C.

Koo5, I.M. Hoffman6, and M.J. Claussen2

1 National Radio Astronomy Observatory, 520 Edgemont Rd, Charlottesville, VA 22903, USA2 National Radio Astronomy Observatory, P. O. Box 0, Socorro, NM 87801, USA3 Jodrell Bank Centre for Astrophysics, Turing Building, University of Manchester, Manchester M13 9PL, UK4 Monash Unversity, Clayton, VIC 3800, Australia5 Astronomy Program, SEES, Seoul National University, Seoul 151-742, South Korea6 Wittenberg University, Springeld, OH 45501, USA

E-mail contact: cbrogan at nrao.edu

We present a comprehensive view of the W51B HII region complex and the W51C supernova remnant (SNR) using newradio observations from the VLA, VLBA, MERLIN, JCMT, and CSO along with archival data from Spitzer, ROSAT,ASCA, and Chandra. Our VLA data include the first 400 cm (74 MHz) continuum image of W51 at high resolution(88′′). The 400 cm image shows non-thermal emission surrounding the G49.2-0.3 HII region, and a compact source ofnon-thermal emission (W51B NT) coincident with the previously-identified OH (1720 MHz) maser spots, non-thermal21 and 90 cm emission, and a hard X-ray source. W51B NT falls within the region of high likelihood for the positionof TeV γ-ray emission. Using the VLBA three OH (1720 MHz) maser spots are detected in the vicinity of W51B NTwith sizes of 60 to 300 AU and Zeeman effect magnetic field strengths of 1.5 to 2.2 mG. The multiwavelength datademonstrate that the northern end of the W51B HII region complex has been partly enveloped by the advancingW51C SNR and this interaction explains the presence of W51B NT and the OH masers. This interaction also appearsin the thermal molecular gas which partially encircles W51B NT and exhibits narrow pre-shock (∆v ∼ 5 km s−1)and broad post-shock (∆v ∼ 20 km s−1) velocity components. RADEX radiative transfer modeling of these twocomponents yield physical conditions consistent with the passage of a non-dissociative C-type shock. Confirmation ofthe W51B/W51C interaction provides additional evidence in favor of this region being one of the best candidates forhadronic particle acceleration known thus far.

Accepted by ApJ


17


The Turbulence Power Spectrum in Optically Thick Interstellar Clouds

Blakesley Burkhart1, A. Lazarian1, V. Ossenkopf2, J. Stutzki2

1 Astronomy Department, University of Wisconsin, Madison, 475 N. Charter St., WI 53711, USA2 Physikalisches Institut der Universität zu Köln, Zulpicher Strasse 77, 50937 Köln, Germany

E-mail contact: burkhart at astro.wisc.edu

The Fourier power spectrum is one of the most widely used statistical tools to analyze the nature of magnetohydro-dynamic turbulence in the interstellar medium. Lazarian & Pogosyan (2004) predicted that the spectral slope shouldsaturate to -3 for an optically thick medium and many observations exist in support of their prediction. However,there have not been any numerical studies to-date testing these results. We analyze the spatial power spectrum ofMHD simulations with a wide range of sonic and Alfvénic Mach numbers, which include radiative transfer effects ofthe 13CO transition. We confirm numerically the predictions of Lazarian & Pogosyan (2004) that the spectral slope ofline intensity maps of an optically thick medium saturates to -3. Furthermore, for very optically thin supersonic COgas, where the density or CO abundance values are too low to excite emission in all but the densest shock compressedgas, we find that the spectral slope is shallower than expected from the column density. Finally, we find that mixedoptically thin/thick CO gas, which has average optical depths on order of unity, shows mixed behavior: for super-Alfvénic turbulence, the integrated intensity power spectral slopes generally follow the same trend with sonic Machnumber as the true column density power spectrum slopes. However, for sub-Alfvénic turbulence the spectral slopesare steeper with values near -3 which are similar to the very optically thick regime.

Accepted by ApJ


The distance to the young open cluster Westerlund 2

Giovanni Carraro1, David Turner2, Daniel Majaess2, and Gustavo Baume3

1 ESO, Alonso de Cordova 3107, 19001, Santiago de Chile, Chile2 Department of Astronomy and Physics, Saint Marys University, Halifax, NS B3H 3C3, Canada3 Facultad de Ciencias Astronómicas y Geof́ısicas (UNLP), Instituto de Astrof́ısica de La Plata (CONICETUNLP),Paseo del Bosque s/n, La Plata, Argentina

E-mail contact: gcarraro at eso.org

A new X-ray, UBVRIc, and JHKs study of the young cluster Westerlund 2 was undertaken to resolve discrepanciestied to the cluster’s distance. Existing spectroscopic observations for bright cluster members and new multi-bandphotometry imply a reddening relation towardsWesterlund 2 described by EU−B/EB−V = 0.63+0.02 EB−V . Variable-extinction analyses for Westerlund 2 and nearby IC 2581 based upon spectroscopic distance moduli and ZAMS fittingyield values of RV = AV /EB−V = 3.88 ± 0.18 and 3.77 ± 0.19, respectively, and confirm prior assertions thatanomalous interstellar extinction is widespread throughout Carina (e.g., Turner 2012). The results were confirmedby applying the color difference method to UBVRIcJHKs data for 19 spectroscopically-observed cluster members,yielding RV = 3.85± 0.07. The derived distance to Westerlund 2 of d = 2.85± 0.43 kpc places the cluster on the farside of the Carina spiral arm. The cluster’s age is no more than τ ∼ 2× 106 yr as inferred from the cluster’s brighteststars and an X-ray (Chandra) cleaned analysis of its pre-main-sequence demographic. Four Wolf-Rayet stars in thecluster core and surrounding corona (WR20a, WR20b, WR20c, and WR20aa) are likely cluster members, and theirinferred luminosities are consistent with those of other late-WN stars in open clusters. The color-magnitude diagramfor Westerlund 2 also displays a gap at spectral type B0.5 V with associated color spread at higher and lower absolutemagnitudes that might be linked to close binary mergers. Such features, in conjunction with the evidence for mass lossfrom the WR stars, may help to explain the high flux of γ rays, cosmic rays, and X-rays from the direction towardsWesterlund 2.

Accepted by A&A


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Observations of gas flows inside a protoplanetary gap

Simon Casassus1, Gerrit van der Plas1, Sebastian Perez M.1, William R.F. Dent2,3, Ed Fomalont4,

Janis Hagelberg5, Antonio Hales2,4, Andrés Jordán6, Dimitri Mawet3, Francois Ménard7,8, Al Wootten4,

David Wilner9, A. Meredith Hughes10, Matthias R. Schreiber11, Julien H. Girard3, Barbara Ercolano12,

Hector Canovas11, Pablo E. Román13, Vachail Salinas1

1 Departamento de Astronomı́a, Universidad de Chile, Casilla 36-D, Santiago, Chile2 Joint ALMA Observatory, Alonso de Córdova 3107, Vitacura 763-0355, Santiago Chile3 European Southern Observatory (ESO), Casilla 19001, Vitacura, Santiago, Chile4 National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903-2475, USA5 Observatoire de Genève, Université de Genève, 51 ch. des Maillettes, 1290, Versoix, Switzerland6 Departamento de Astronomı́a y Astrof́ısica, Ponticia Universidad Católica de Chile Santiago, Chile7 UMI-FCA, CNRS / INSU France (UMI 3386) , and Departamento de Astronomı́a, Universidad de Chile, Santiago,Chile8 CNRS / UJF Grenoble 1, UMR 5274, Institut de Planétologie et dAstrophysique de Grenoble (IPAG), France9 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 USA10 Department of Astronomy, U. C. Berkeley, 601 Campbell Hall, Berkeley, CA 9472011 Departamento de F́ısica y Astronomı́a, Universidad Valparaiso, Av. Gran Bretana 111, Valparaiso, Chile12 University Observatory, Ludwig-Maximillians University, Munich13 Center of Mathematical Modeling, University of Chile, Av. Blanco Encalada 2120 Piso 7, Santiago, Chile

E-mail contact: scasassus at u.uchile.cl

Gaseous giant planet formation is thought to occur in the first few million years following stellar birth. Models predictthat giant planet formation carves a deep gap in the dust component (shallower in the gas). Infrared observationsof the disk around the young star HD142527, at ∼140 pc, found an inner disk ∼10 AU in radius, surrounded by aparticularly large gap, with a disrupted outer disk beyond 140AU, indicative of a perturbing planetary-mass body at∼90 AU. From radio observations, the bulk mass is molecular and lies in the outer disk, whose continuum emissionhas a horseshoe morphology. The vigorous stellar accretion rate would deplete the inner disk in less than a year, soin order to sustain the observed accretion, matter must flow from the outer-disk into the cavity and cross the gap.In dynamical models, the putative protoplanets channel outer-disk material into gap-crossing bridges that feed stellaraccretion through the inner disk. Here we report observations with the Atacama Large Millimetre Array (ALMA)that reveal diffuse CO gas inside the gap, with denser HCO+ gas along gap-crossing filaments, and that confirm thehorseshoe morphology of the outer disk. The estimated flow rate of the gas is in the range 7× 10−9 to 2× 10−7 M⊙yr−1, which is sufficient to maintain accretion onto the star at the present rate.

Accepted by Nature


Alignment Between Flattened Protostellar Infall Envelopes and Ambient MagneticFields

Nicholas L. Chapman1, Jacqueline A. Davidson2, Paul F. Goldsmith3, Martin Houde4,5, Woojin Kwon6,7,

Zhi-Yun Li8, Leslie W. Looney6, Brenda Matthews9,10, Tristan G. Matthews1, Giles Novak1, Ruisheng

Peng11, John E. Vaillancourt12, Nikolaus H. Volgenau13

1 Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA) & Dept. of Physics & Astronomy,Northwestern University, 2145 Sheridan Road, Evanston, IL 60208, USA2 School of Physics, University of Western Australia, 35 Stirling Hwy, Crawley, WA 6009, Australia3 Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, MS 264-782, Pasadena, CA91109, USA4 Department of Physics and Astronomy, University of Western Ontario, London, ON, Canada5 Division of Physics, Mathematics and Astronomy, California Institute of Technology, Pasadena, CA 91125, USA6 Department of Astronomy, University of Illinois, 1002 West Green Street, Urbana, IL 61801, USA7 SRON Netherlands Institute for Space Research, Landleven 12, 9747 AD, Groningen, The Netherlands8 Astronomy Department, University of Virginia, Charlottesville, VA 22904, USA9 Herzberg Institute of Astrophysics, National Research Council of Canada, 5071 West Saanich Road, Victoria, BC

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V9E 2E7, Canada10 Department of Physics and Astronomy, University of Victoria, 3800 Finnerty Road, Victoria, BC V8P 1A1, Canada11 Caltech Submillimeter Observatory, 111 Nowelo Street, Hilo, HI 96720, USA12 SOFIA Science Center, Universities Space Research Association, NASA Ames Research Center, MS 232-11, MoffettField, CA 94035, USA 13 California Institute of Technology, Owens Valley Radio Observatory, Big Pine, CA 93513,USA

E-mail contact: nchapman at u.northwestern.edu

We present 350 µm polarization observations of four low-mass cores containing Class 0 protostars: L483, L1157,L1448-IRS2, and Serp-FIR1. This is the second paper in a larger survey aimed at testing magnetically regulatedmodels for core-collapse. One key prediction of these models is that the mean magnetic field in a core should bealigned with the symmetry axis (minor axis) of the flattened YSO inner envelope (aka pseudodisk). Furthermore, thefield should exhibit a pinched or hour-glass shaped morphology as gravity drags the field inward towards the centralprotostar. We combine our results for the four cores with results for three similar cores that were published in the firstpaper from our survey. An analysis of the 350 µm polarization data for the seven cores yields evidence of a positivecorrelation between mean field direction and pseudodisk symmetry axis. Our rough estimate for the probability ofobtaining by pure chance a correlation as strong as the one we found is about 5%. In addition, we combine togetherdata for multiple cores to create a source-averaged magnetic field map having improved signal-to-noise ratio, and thismap shows good agreement between mean field direction and pseudodisk axis (they are within 15◦). We also see hintsof a magnetic pinch in the source-averaged map. We conclude that core-scale magnetic fields appear to be strongenough to guide gas infall, as predicted by the magnetically regulated models. Finally, we find evidence of a positivecorrelation between core magnetic field direction and bipolar outflow axis.

Accepted by ApJ


Structure and radial equilibrium of filamentary molecular clouds

Yanett Contreras1,2, Jill Rathborne1 and Guido Garay2

1 CSIRO Astronomy and Space Science, PO Box 76, Epping NSW 1710, Australia2 Departamento de Astronomia, Universidad de Chile, Casilla 36-D, Santiago, Chile

E-mail contact: yanett.contreras at csiro.au

Recent dust continuum surveys have shown that filamentary structures are ubiquitous along the Galactic plane. Whilethe study of their global properties has gained momentum recently, we are still far from fully understanding their originand stability. Theories invoking magnetic field have been formulated to help explain the stability of filaments; however,observations are needed to test their predictions. In this paper, we investigate the structure and radial equilibrium offive filamentary molecular clouds with the aim of determining the role that magnetic field may play. To do this, we usecontinuum and molecular line observations to obtain their physical properties (e.g. mass, temperature and pressure).We find that the filaments have lower lineal masses compared to their lineal virial masses. Their virial parametersand shape of their dust continuum emission suggests that these filaments may be confined by a toroidal dominatedmagnetic field.

Accepted by MNRAS

http://adsabs.harvard.edu/doi/10.1093/mnras/stt720

Simulated Observations of Young Gravitationally Unstable Protoplanetary Discs

Tom Douglas1, Paola Caselli1, John Ilee2,1, Aaron Boley3, Tom Hartquist1, Richard Durisen4 and

Jonathan Rawlings5

1 chool of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, UK2 School of Physics and Astronomy, University of St Andrews, North Haugh, St Andrews, KY16 9SS, UK3 Department of Astronomy, University of Florida, 211 Bryant Space Center, PO Box 112055, USA4 Department of Astronomy, Indiana University, 727 East 3rd Street, Swain West 319, Bloomington, IN 47405, USA5 Department of Physics & Astronomy, University College London, London WC1E 6BT, UK

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http://arxiv.org/pdf/1305.2922http://adsabs.harvard.edu/doi/10.1093/mnras/stt720

E-mail contact: pytd at leeds.ac.uk

The formation and earliest stages of protoplanetary discs remain poorly constrained by observations. ALMA will soonrevolutionise this field. Therefore, it is important to provide predictions which will be valuable for the interpretationof future high sensitivity and high angular resolution observations. Here we present simulated ALMA observationsbased on radiative transfer modelling of a relatively massive (0.39 solar masses) self-gravitating disc embedded in a 10solar mass dense core, with structure similar to the pre-stellar core L1544. We focus on simple species and concludethat C17O 3-2, HCO+ 3-2, OCS 26-25 and H2CO 404-303 lines can be used to probe the disc structure and kinematicsat all scales.

Accepted by MNRAS


The distance to the young open cluster Westerlund 2

R. Errmann1, R. Neuhäuser1, L. Marschall2, G. Torres3, M. Mugrauer1, W.P. Chen4, S.C.-L. Hu4,5,

C. Briceno6, R. Chini7,8, L. Bukowiecki9, D.P. Dimitrov10, D. Kjurkchieva11, E.L.N. Jensen12, D.H.

Cohen12, Z.-Y. Wu13, T. Pribulla14, M. Vanko14, V. Krushevska15, J. Budaj14, Y. Oasa16, A.K. Pandey17,

M. Fernandez18, A. Kellerer19, and C. Marka1

1 Astrophysikalisches Institut und Universitäts-Sternwarte Jena, Schillergäßchen 2-3, D-07745 Jena, Germany2 Gettysburg College Observatory, Department of Physics, 300 North Washington St., Gettysburg, PA 17325, USA3 Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Mail Stop 20, Cambridge MA 02138, USA4 Graduate Institute of Astronomy, National Central University, Jhongli City, Taoyuan County 32001, Taiwan (R.O.C.)5 Taipei Astronomical Museum, 363 Jihe Rd., Shilin, Taipei 11160, Taiwan6 Centro de Investigaciones de Astronomia, Apartado Postal 264, Merida 5101, Venezuela7 Astronomisches Institut, Ruhr-Universität Bochum, Universitätsstr. 150, D-44801 Bochum, Germany8 Instituto de Astronomı́a, Universidad Católica del Norte, Antofagasta, Chile9 Toruń Centre for Astronomy, Nicolaus Copernicus University, Gagarina 11, PL87-100 Toruń, Poland10 Institute of Astronomy and NAO, Bulg. Acad. Sci., 72 Tsarigradsko Chaussee Blvd., 1784 Soa, Bulgaria11 Shumen University, 115 Universitetska str., 9700 Shumen, Bulgaria12 Dept. of Physics and Astronomy, Swarthmore College, Swarthmore, PA 19081-1390, USA13 Key Laboratory of Optical Astronomy, NAO, Chinese Academy of Sciences, 20A Datun Road, Beijing 100012,China14 Astronomical Institute, Slovak Academy of Sciences, 059 60, Tatranská Lomnica, Slovakia15 Main Astronomical Observatory of National Academy of Sciences of Ukraine, 27 Akademika Zabolotnoho St., 03680Kyiv, Ukraine16 Dept. of Astronomy and Earth Science, Saitama University, 255 Shimo-Okubo, Sakura, Saitama 338-8570, Japan17 Aryabhatta Research Institute of Observational Science, Manora Peak, Naini Tal, 263 129, Uttarakhand, India18 Instituto de Astrosica de Andalucia, CSIC, Apdo. 3004, 18080 Granada, Spain19 Department of Physics, Durham University, South Road, Durham DH1 3LE, United Kingdom

E-mail contact: ronny.errmann at uni-jena.de

With an apparent cluster diameter of 1.5◦ and an age of ∼ 4 Myr, Trumpler 37 is an ideal target for photometricmonitoring of young stars as well as for the search of planetary transits, eclipsing binaries and other sources ofvariability. The YETI consortium has monitored Trumpler 37 throughout 2010 and 2011 to obtain a comprehensiveview of variable phenomena in this region. In this first paper we present the cluster properties and membershipdetermination as derived from an extensive investigation of the literature. We also compared the coordinate list tosome YETI images. For 1872 stars we found literature data. Among them 774 have high probability of being memberand 125 a medium probability. Based on infrared data we re-calculate a cluster extinction of 0.9 – 1.2 mag. We canconfirm the age and distance to be 3 – 5 Myr and ∼ 870 pc. Stellar masses are determined from theoretical modelsand the mass function is fitted with a power-law index of α = 1.90(0.1− 0.4M⊙) and α = 1.12(1− 10M⊙).

Accepted by Astronomische Nachrichten


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A Study of starless dark cloud LDN 1570: Distance, Dust properties and Magnetic fieldgeometry

C. Eswaraiah1, G. Maheswar1,2, A.K. Pandey1, J. Jose3, A.N. Ramaprakash4, H.C. Bhatt3

1 Aryabhatta Research Institute of Observational Sciences, Manora Peak, Nainital 263 129, India2 Korea Astronomy and Space Science Institute, 61-1, Hwaam-dong, Yuseong-gu, Daejeon 305-348, Republic of Korea3 Indian Institute of Astrophysics, II Block, Koramangala, Bangalore 560 034, India4 Inter-University Centre for Astronomy and Astrophysics, Ganeshkhind, Pune 411007, India

E-mail contact: eswarbramha at gmail.com

We wish to map the magnetic field geometry and to study the dust properties of the starless cloud, L1570, usingmulti-wavelength optical polarimetry and photometry of the stars projected on the cloud. We made R-band imagingpolarimetry of the stars projected on a cloud, L1570, to trace the magnetic field orientation. We also made multi-wavelength polarimetric and photometric observations to constrain the properties of dust in L1570. We estimated adistance of 394±70 pc to the cloud using 2MASS JHKs colours. Using the values of the Serkowski parameters namelyσ1, ǭ, λmax and the position of the stars on near infrared color-color diagram, we identified 13 stars that could possiblyhave intrinsic polarization and/or rotation in their polarization angles. One star, 2MASS J06075075+1934177, whichis a B4Ve spectral type, show the presence of diffuse interstellar bands in the spectrum apart from showing Hα linein emission. There is an indication for the presence of slightly bigger dust grains towards L1570 on the basis of thedust grain size-indicators such as λmax and Rv values. The magnetic field lines are found to be parallel to the cloudstructures seen in the 250 µm images (also in 8 µm and 12 µm shadow images) of L1570. Based on the magnetic fieldgeometry, the cloud structure and the complex velocity structure, we believe that L1570 is in the process of formationdue to the converging flow material mediated by the magnetic field lines. Structure function analysis showed that inthe L1570 cloud region the large scale magnetic fields are stronger when compared with the turbulent component ofmagnetic fields. The estimated magnetic field strengths suggest that the L1570 cloud region is sub-critical and hencecould be strongly supported by the magnetic field lines.

Accepted by A&A


Mass and motion of globulettes in the Rosette Nebula

G. F. Gahm1, C. M. Persson2, M. M. Mäkelä3 and L. K. Haikala3

1 Stockholm Observatory, AlbaNova University Centre, Stockholm University, SE-106 91 Stockholm, Sweden2 Chalmers University of Technology, Department of Earth and Space Sciences, Onsala Space Observatory, SE-439 92Onsala, Sweden3 Department of Physics, PO Box 64, FI-00014 University of Helsinki, Finland

E-mail contact: gahm at astro.su.se

We have investigated tiny molecular clumps in the Rosette Nebula. In optical images these objects, so-called globulettes,appear as dark patches against the background of bright nebulosity. Radio observations were made of molecular lineemission from 16 globulettes identified in a previous optical survey. In addtion, we collected images in the NIR broad-band JHKs and narrow-band Paschen β and H2. Practically all globulettes were detected in our CO survey. Theobserved 12CO (3–2) and (2–1) line temperatures range from 0.6 K to 6 K, the 13CO being a third of this. As a rulethe lines are narrow, ∼ 1.0 kms−1.Ten objects, for which we collected information from several transitions in 12CO and 13CO were modelled using aspherically symmetric model. The best fit to observed line ratios and intensities was obtained by assuming a modelcomposed of a cool and dense centre and warm and dense surface layer. This model provides estimates of maximumand minimum mass; the average masses range from about 50 to 500 Jupiter masses, which is similar to earlierestimates based on extinction measures. The globulettes selected are dense, nH ∼ 10

4 cm−3, with very thin layers offluorescent H2 emission, showing that the gas is in molecular form just below the surface. The NIR data shows thatseveral globulettes are very opaque and contain dense cores. Internal gas motions are weak, but some larger objectsshow velocity-shifted components associated with tails. However, most globulettes do not show any signs of tails orpronounced bright rims. Because of the high density encountered already at the surface, the rims become thin, asevidenced by our Pβ images, which also show extended emission, that most likely comes from the backside of the

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globulettes.We conclude that the entire complex of shells, elephant trunks, and globulettes in the northern part of the nebula isexpanding with nearly the same velocity of ∼ 22 km s−1, and with a very small spread in velocity among the globulettes.Some globulettes are in the process of detaching from elephant trunks and shells, while other more isolated objectsmust have detached long ago and are lagging behind in the general expansion of the molecular shell. We envision thatafter detachment the objects erode to isolated and dense clumps. The suggestion that some globulettes might collapseto form planetary-mass objects or b

the star formation newsletterreipurth/newsletter/newsletter246.pdfafter my phd i took a trip to...

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