the unidentified fuv lines of hydrogen deficient dwarfs

DEPARTMENT OF PHYSICS AND ASTRONOMY

PhD Recruitment Day – 31PhD Recruitment Day – 31stst Jan 2007 Jan 2007

The unidentified FUV lines of hydrogen deficient dwarfs

David BoyceDavid BoyceM. A. Barstow, J. K. BarstowM. A. Barstow, J. K. Barstow

F. James, R. Laird, P. DobbieF. James, R. Laird, P. Dobbie

A. Forbes, J. Aston, B. BoolesA. Forbes, J. Aston, B. Booles


The unsolved problem of EUV The unsolved problem of EUV

deficiencydeficiency DO white dwarfs are significantly EUV deficientDO white dwarfs are significantly EUV deficient

To reduce the predicted EUV flux, without increasing the assumed elemental To reduce the predicted EUV flux, without increasing the assumed elemental abundances above the values determined from IUE and HST spectra, it is abundances above the values determined from IUE and HST spectra, it is necessary to find an alternative source of photospheric opacity.necessary to find an alternative source of photospheric opacity.

A possible source could be from additional, as yet undetected elements that are A possible source could be from additional, as yet undetected elements that are not currently included in the theoretical model calculations. not currently included in the theoretical model calculations.

The DO line problemThe DO line problem

The FUV spectra of DO white dwarfs contain more unidentified lines than The FUV spectra of DO white dwarfs contain more unidentified lines than identified ones.identified ones.

The result of incomplete and inaccurate atomic data?The result of incomplete and inaccurate atomic data?

Introduction


Solutions for the DO line problemSolutions for the DO line problem

1.1. Unidentified lines belong to high ionisation/ excitation species not included in Unidentified lines belong to high ionisation/ excitation species not included in the spectral line lists.the spectral line lists.

2.2. Unidentified lines belong to iron group and post iron group species not Unidentified lines belong to iron group and post iron group species not included in the spectral line lists.included in the spectral line lists.

3.3. Unidentified lines belong to a species wholly unexpected to be present in the Unidentified lines belong to a species wholly unexpected to be present in the DO.DO.

Introduction


Processing and candidate selectionProcessing and candidate selection

All hydrogen deficient dwarfs were obtained from MAST and processed in the usual way (Barstow et al All hydrogen deficient dwarfs were obtained from MAST and processed in the usual way (Barstow et al

2003).2003).

The data has been calibrated using the calfuse pipeline version 2.0.5 or later, resulting in several spectra (covering different wavelength segments) per FUSE exposure. The exposures for each segment are then co-added, weighting each according to exposure time, and finally the segments are combined, weighted by their signal-to-noise ratio, to produce a single spectrum

Stars badly effected by molecular hydrogen were thrown out

Data reduction


A two component mysteryA two component mystery

1.1. The ISM contributes a complex The ISM contributes a complex and poorly understood and poorly understood component to the DO spectra.component to the DO spectra.

2.2. This component is not exactly This component is not exactly the same as in the more the same as in the more familiar DA spectrafamiliar DA spectra

3.3. How many of the unidentified How many of the unidentified lines that were previously lines that were previously thought to be photospheric thought to be photospheric originate in fact from the ISM?originate in fact from the ISM?

Introduction


Velocity discrimination; the basic Velocity discrimination; the basic ideaidea

Line velocity

Average photospheric velocity

Average ISM velocity

Sta

r 1

Sta

r 1

Sta

r 2

Sta

r 2

Sta

r 1

Line position

Sta

r 2

Sta

r 2

Velocity Discrimination


Velocity discrimination; real starsVelocity discrimination; real stars

From well known lines we know an average velocity for the star and the ISM in that direction

Pho

tosp

heric

ISM

Pho

tosp

heric

ISM

Line=photospheric

Pho

tosp

heric

ISM

Line=ISM

Graph of predicted lab wavelength

Using multiple stars we can differentiate between an unknown line being Photospheric or ISM without even knowing what it is.

vc

c

0



Velocity Velocity discrimination; the discrimination; the

resultsresults1.1. Velocity discrimination clearly Velocity discrimination clearly

separates ISM lines from separates ISM lines from photospheric linesphotospheric lines

2.2. Origin of lines found without Origin of lines found without knowing line identityknowing line identity



A side note about O A side note about O VIVI

O VI in FUV spectra of white dwarfs considered O VI in FUV spectra of white dwarfs considered to be tracers of hot gas in the interstellar to be tracers of hot gas in the interstellar mediummedium

Since the distance to white dwarfs puts them Since the distance to white dwarfs puts them just inside, on or just outside the “hot local just inside, on or just outside the “hot local bubble” we can test the origin of the O VI using bubble” we can test the origin of the O VI using velocity discrimination.velocity discrimination.

Our results show that all O VI detected along Our results show that all O VI detected along the lines of sights of stars within the local the lines of sights of stars within the local bubble had O VI of a stellar origin.bubble had O VI of a stellar origin.

The hot local bubble = The cold The hot local bubble = The cold local bubble local bubble



Finding the photospheric velocityFinding the photospheric velocity

From a large sample ofFrom a large sample of

identified lines an averageidentified lines an average

photospheric velocity canphotospheric velocity can

be calculated.be calculated.

Lines common to DOs and Lines common to DOs and

DAs can be used for thisDAs can be used for this

However Hot DOs and However Hot DOs and

PG1159 stars are a problemPG1159 stars are a problem

due to the lack of linesdue to the lack of lines

common to DAs common to DAs

Makes velocity discriminationMakes velocity discrimination

harderharder

Finding the photospheric velocity for DOs


A new approach to finding the A new approach to finding the photospheric velocity photospheric velocity

933.378 N III -5.7767

933.384 S VI -7.7007

933.383 Ni VI -7.38

933.383 Ni VI -7.38

933.265 Co V 30.458

933.5 Co V -44.897

1031.91 O VI -9.2815

1031.72 Ni VI 46.1173

1031.72 Ni Vi 46.1173

1031.8 Ni VI 24.0738

1031.87 Co V 2.32037

1031.92 Fe II -12.472

Velocity Velocity



Recurrent velocity analysis; DA starsRecurrent velocity analysis; DA stars

Using the Morton line list we Using the Morton line list we

observe in the DA that there observe in the DA that there is is

peaks at the ISM andpeaks at the ISM and

photospheric velocityphotospheric velocity

Changing to the Kurucz line Changing to the Kurucz line listlist

Increases the recurrence of Increases the recurrence of

The photospheric velocityThe photospheric velocity

Kurucz more complete for Kurucz more complete for

higher ionisations higher ionisations



Recurrent velocity analysis; DO starsRecurrent velocity analysis; DO stars

Using either Morton or Using either Morton or Kurucz Kurucz

We do not retrieve the We do not retrieve the

photospheric velocity.photospheric velocity.

The unidentified lines thatThe unidentified lines that

make up DOs and PG1159 make up DOs and PG1159 stars stars

are not in the Morton or the are not in the Morton or the

Kurucz line list. Kurucz line list.

No amount of looking will No amount of looking will solve solve

The DO line problem.The DO line problem.



Results of velocity searchResults of velocity searchUsing these methods a photospheric velocity is found for a broad range of DOs and PG1159 stars

Using the photospheric velocity for DO line identification

Star name Photospheric velocity

Spectral type Temperature

PG1144+005 4.3 PG1159 150000K

PG1424+535 -15.7 Cool PG1159 110000K

PG1707+427 -40.1 Cool PG1159 85000K

WD0109+111 28.8 DO 75000K

WD1034+001 41.3 DO 100000K

WD1159-034 42.5 DO/PG1159 140000K

WD1202+608 -64 sDO (d degen) 58000K

WD0501-289 18.5 DO 70000K


High ionisation/excitation speciesHigh ionisation/excitation species

7/8

4/4

Generation of atomic data for high ionisation species is making progressGeneration of atomic data for high ionisation species is making progress

3/8

2/5

Some lines however not so well behavedSome lines however not so well behaved

Success rate



Post iron groupPost iron group

A considerable number of A considerable number of identifications of post iron group identifications of post iron group elements in the FUV spectra of elements in the FUV spectra of cool DOs have been put forward cool DOs have been put forward by Chayer et al 2005 by Chayer et al 2005

Do these lines appear in any of Do these lines appear in any of our stars?our stars?

Do these lines occupy the correct Do these lines occupy the correct velocity?velocity?

Chayer et al 2005Chayer et al 2005



Post iron groupPost iron group

Species line Velocity? Photospheric?

As IV 946.5 Fail

As IV 953.3 Pass Fail

As IV 956.9 Fail

As IV 971.1 Fail

As IV 980.6 Fail

As IV 999.3 Pass Pass

As IV 1003.4 Fail


Lines tested against photospheric velocity of starLines tested against photospheric velocity of star

Lines that fail the testLines that fail the test

Species Passes Total

As IV 1 7

As V 2 4

Se III 1 2

Se IV 0 7

Se V 0 2

Br VI 0 1

Sn IV 2 4

Te VI 1 2

I V 0 5

I VI 0 1


ConclusionsConclusions

Velocity discrimination allows us to identify ISM lines from Velocity discrimination allows us to identify ISM lines from photospheric linesphotospheric lines

Unknown lines not in linelistsUnknown lines not in linelists

Post iron group species do not occur at detectable levels.Post iron group species do not occur at detectable levels.

Velocity forms a powerful tool in testing line identitiesVelocity forms a powerful tool in testing line identities

High excitation elements such as Ne VIII are the best High excitation elements such as Ne VIII are the best candidates for the additional opacity required to solve the EUV candidates for the additional opacity required to solve the EUV deficit.deficit.

the unidentified fuv lines of hydrogen deficient dwarfs

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