may 19-23bologna pg course evening zl guilleman: “the heavens” 1896 interstellar and...

May 19-23 Bologna pg course

Evening ZL Guilleman: “The Heavens”

1896

Interstellar and interplanetary dust

Michael Rowan-Robinson Imperial College


Interstellar dust

• Reviews of interstellar dustSavage and Mathis 1979 ARAA

Mathis 1990 ARAADraine 2003 ARAATielens 2008 ARAA, PAHs


Historical background• 1930 Trumpler deduced presence of interstellar dust from apparent decrease in angular size of open clusters with distance. He also noticed that more distant stars were redder.

• 1930-48 Stebbins, also in collaboration with Whitford, derived the interstellar dust reddening law A ≈ 1/

• 1969 Woolf and Ney discovered 10 m broad emission feature, suggested due to silicates. Gilman (1969) showed that in outflows from oxygen-rich M stars would expect formation of silicates, while in carbon rich C stars would expect graphite.

• 1970s uv studies found 2200 Å feature, due to graphite ?

• modeling the spectral energy distributions (SEDs) of these circumstellar dust shells pointed to presence of amorphous silicates around M stars and amorphous carbon around carbon stars (RR & Harris 1983)


Circumstellar dust shells

M stars

R-R &Harris1983a

C stars

R-R &Harris1983b


Models for interstellar grains

Mathis et al (1977) constructed a model for interstellar extinction based on a mixture of silicate and graphite particles with a continuous range of sizes from 0.005 – 0.25 m.

Draine and Lee (1984) made an important improvement to this model by calculating the absorption and scattering efficiencies of each species from the dielectric constants for the materials.However for ‘astronomical silicates’ they had to effectively derive the optical constants for the mid infrared (5-30 m)from the empirically derived extinction curve.


Model for interstellar grains based on c.d.s.

Rowan-Robinson (1986) proposed a model for interstellar grains consisting of 0.1 m amorphous silicates and 0.1 m amorphous carbon grains (based on modeling of circumstellar dust shells), plus smaller graphite and silicate grains to fit uv extinction. Model was tweaked in R-R (1992).


Main ingredients of interstellar dust

• Amorphous silicates (9.7 and 18 m features)• Amorphous carbon• Polycyclic Aromatic Hydrocarbons 3.3, 6.2, 7.7, 8.6, 11.3 m)– also responsible for 2175 A feature ?– also responsible for diffuse interstellar bands (0.38-0.87 m) ?

• Graphite ? (2175 A)• Aliphatic hydrocarbon mantles (3.4 m)• Ices (3.1 m (H20), 4.6 m (XCN), 4.67 m (CO) etc)

• Spinning grains• Crystalline silicates

– In some environments


Interstellar extinction

Draine 2003


PAHs

1973 Gillett et al: found unidentified broad emission features at 3.3, 6.2, 7.7, 8.6 and 11.25 m

a related phenomenon was diffuse mid-infrared radiation around bright stars, which had to come from some kind of transient grain (Sellgren 1984)

explained as due to large molecules or very small grains ofpolycyclic aromatic hydrocarbons, PAHs (Leger & Puget 1984,Allamandola et al 1985) – grain absorbs a uv photon, is heated to a very high temperature and then rapidly cools


PAHs

Tielens 2008Features in Orion Bar and NGC 7027, labelled with relevant C/H bond


PAHs

L: 3 identified components in ISO spectrum of NGC 7023R: spatial distribution of ionic (blue), neutral PAHs (green), clusters (red)


PAHs

Dependence of PAH strength on O/H abundance


Grain size distribution


Polarization of starlight

Starlight is observed to be linearly polarized, with a dependence on wavelength

p() = pmax exp{ - K ln(/max)2}, with max ~ 5500 A

Explained as due to alignment of interstellar grains by the Galactic magnetic field (Davis and Greenstein 1951). Grains have to be elongated and then precess around the field direction.

For very small grains this spinning can explain excess emission seen at wavelengths ~ 1 cm.


Where do interstellar grains originate ?

Anders & Zinner (1993) review isotopic abundance analysis of meteoritic inclusions

conclude that they can identify interstellar grains, from a variety of sources: AGB stars (red giants), supernovae, Wolf-Rayet stars (high-mass stars undergoing mass-loss

molecular mantles presumably form (and are destroyed) in molecular clouds


Predicted extinction and scattering


Spinning grains

Spinning grains proposed to explain anomalous cm radiation (electric dipole rotational emission from very small grains) Draine & Lazarin 1998

Evidence from the Planck team (XX, 2011) for spinning grains in the Perseus molecular cloud


Observed ir emission from Milky Way

May 19-22, 2014 Bologna

Crystalline silicates

The ISO mission, with its excellent spectroscopic capability, demonstrated that in certain environments, eg ULIRGs, QSOs, young and old stars in our Galaxy, traces of crystalline silicates could be detected.Previously thought that silicates in ism and in extragalactic sources were amorphous (<2% crystalline).Crystalline silicates are common, of course in the solar system.

Formed in winds from AGB stars and in winds from QSOs.


Interplanetary dust

Evening Zodiacal Light photographed by Brian May in Tenerife 1971


Jones & Rowan-Robinson Fan & Band model

Jones & Rowan-Robinson (1993) fan+bands model model

Ingredients:• fan to 1.5 au, density r-1 f(), f() = (cos )Q exp{ –P sin||• two pairs of bands, corresponding to Eos and Themis families• additional ingredient of broad bands at | ~ 10o • each component has its own symmetry plane (, i)• problem was that asteroidal bands could only account for 25% of dust in fan (rest cometary ?)


A major ingredient – cometary dust

Spitzer image of debris shed along a cometary orbit


Kelsall et al 1998

COBE: Kelsall et al (1998)


Kelsall et al 1998

COBE: Kelsall et al (1998)

•Kelsall et al 1998: multi-parameter fit to DIRBE data

• fan to 5.2AU, so column density jumps up at 1.5AU• T=286 K but emissivity modified at 60-240 m• dens as r-1.3 (required if have fan going much beyond 1.5AU)• model asteroidal dust bandsbut no specific cometary component• new component (found inIRAS data) – solar ring at 1au + trailing blob


Kelsall et al 1998

ULYSSES, 1990-2009

• Ulysses spacecraft, en route to Jupiter, directly detected fast-moving dust component, attributed to interstellar dust

Mann 2010

Divine 1993


Kelsall et al 1998

Flow of interstellar dust into inner solar system

Grogan et al (1996) dynamical simulation of flow of interstellar dust into inner solar system: • small grains repelled from downstream cylinder by radiation pressure• large grains focused behind Sun by Hoyle-Lyttleton accretion (HL rad~4au)

Mann 2010


Kelsall et al 1998

Time scales

Time-scale for asteroidal dust, in approximately circular orbits, to spiral inwards to Sun, under action of Poynting-Robertson drag: ~10,000 years(Gustafsen et al 1987)

Time-scale for interstellar dust to traverse ~200 au from the magnetopause:~50 years

• expect vertical density profile of cometary (and Kuiper belt ?) dust to be modified at orbits of Jupiter and Mars

• expect vertical density profile of asteroidal dust to be modified at orbit of Mars

• interstellar dust unaffected by planets, larger grains within H-L column will be gravitationally focused behind Sun, may just fall into back side of Sun. May expect variations in i.s. dust density in inner Solar System on time-scale of years, as solar cycle variations at magnetopause control entry of i.s. dust


New zodiacal dust model[Rowan-Robinson and May 2013] • starting point: Jones and RR (1993)

• fan to r=1.5AU, bands to 3.1 AU• T(1AU) = 255 K• dens as r-1.3

• include 1 au solar ring, and trailing blob

• model cometary dust as additional fan component to 30AU, dens as r-1

• model interstellar dust as isotropic additional component, density constant

• retune fan and bands parameters, searching for minimum in 2

(outer narrow bands now assumed to be Veritas family (Grogan et al 2001))

• fit to both IRAS and DIRBE data. We used all data in IRAS HCON1 with |b| > 40o,and 69 ‘good’ days of DIRBE data with |b| > 40o (20 times as much DIRBE data as used by Kelsall et al)


IRAS zodi scans at 12, 25, 60 100m


zodi scan at 25 m, fan subtracted


COBE scans at 4.9, 12, 25, 60, 100 m

Data from Jan 19th 1990.

Solar elongation = 90o

|b| > 40o


COBE scans at 4.9, 12, 25, 60, 100 m:

solar elongation = 70o and 110o

70o 110o

model still works well at extreme solar elongations


2 versus interstellar dust density

Both IRAS and DIRBE data have minimum reduced 2 at same value of interstellar dust density


radial variation of dust density

At 1.5 au, relative contribution of integrated (over ) dust-density to fan density is:

cometary 70.4% asteroidal 22.2% interstellar 7.5%

Mass-density of interstellar dust in ecliptic plane ~ 10-25.0 gm/cc, cf 10-25.3+-0.7 estimated by Kimaru et al (2003) from Ulysses data at 1.5 au


zodi scan at 25 m, fan subtracted

- models with fan extending to 5.2au

Kelsall fan, no isd JRR fan to 5.2au + isd


summary on zodiacal dust• Jones and RR1993 model P=2.85, Q=8, 2 = 5.03 for IRAS

• revised JRR (P=2.12, Q=10.2) fan to 1.5au, dens as r-1.3, revised narrow and broad bands, plus cometary dust from 1.5 to 30 AU (P=2.5), solar ring and trailing blob (reduced amplitude cf Kelsall), interstellar dust (isotropic and uniform) from 0 to 30 au, 2 = 1.83 for IRAS, 1.28 for DIRBE

• extend fan to 5.2 au at 0.85 of r<1.5 density (P=2.5, Q=3.5), revised bands, ring +blob, no cometary, interstellar dust (lower density), 2 = 2.48 for IRAS,

1.33 for DIRBE

• Kelsall fan to 5.2 au, narrow bands, ring+blob, no cometary or isd, 2 = 3.40 for IRAS, 1.31 for DIRBE

• extending fan to 5.2 au does not improve fit. Also tested idea that broad bands originate in Kuiper belt, but did not improve fit

• interstellar dust appears to be present at amplitude ~1% of density of fan at r = 1au.


Reviews, citations and the astronomical

literatureA few thoughts about how to find your way round the astronomical literature:

• the 50 volumes of Annual Reviews of Astronomy and Astrophysics provide a superb series of reviews of different aspects of the field. You should check at least the past ten years to see if there’s a review on what you’re working on.

• citations are a useful guide to which papers you can not afford to miss.

• http://astro.ic.ac.uk/public/mrr/NightVisionpapers.pdf gives a list of 412 papers on infrared and submillimetre astronomy (excluding CMB) with more than 200 citations up to Nov 2009 (compiled for my history of infrared astronomy ‘Night Vision’)

• You don’t have to read them all ! Papers on interstellar dust and on stars seem to attract inordinate numbers of citations. But there are many great papers here.

http://astro.ic.ac.uk/public/mrr/NightVisionpapers.pdf


Reviews, citations and the astronomical

literature (cont.)If you know of a paper on a particular topic and you want to check if anything more recent has been written on the same topic, you search for the paper on the NASA-ADS database, first clicking on ‘sort by citation counts’ on the front page.

When you find the paper, click on it and then click on ‘citations to the article’ on the menu.

You will then get a list of all the papers that have cited the original article.

Hopefully some of these will be more recent papers on the same topic.

It’s not foolproof because not everyone is careful about referencing earlier articles on the same topic.

But I find this a useful way of getting up to date.


these lectures online

The first two lectures are online at:

http://astro.ic.ac.uk/public/mrr/lectures/Bologna1.irhistory.ppt

and

http://astro.ic.ac.uk/public/mrr/lectures/Bologna2.dust.ppt





may 19-23bologna pg course evening zl guilleman: “the heavens” 1896 interstellar and...

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