J/MNRAS/483/2941 Multiwavelength observations of GD 394 (Wilson+, 2019)
Multiwavelength observations of the EUV variable metal-rich white dwarf GD 394.
Wilson D.J., Gansicke B.T., Koester D., Toloza O., Holberg J.B.,
Preval S.P., Barstow M.A., Belardi C., Burleigh M.R., Casewell S.L.,
Cauley P.W., Chote P., Farihi J., Hollands M.A., Long K.S., Redfield S.
<Mon. Not. R. Astron. Soc., 483, 2941-2957 (2019)>
=2019MNRAS.483.2941W 2019MNRAS.483.2941W (SIMBAD/NED BibCode)
ADC_Keywords: Stars, variable ; Stars, white dwarf ; Spectra, ultraviolet ;
Spectra, optical
Keywords: circumstellar matter - stars: individual: GD 394 -
stars: variables: general - white dwarfs
Abstract:
We present new Hubble Space Telescope (HST) ultraviolet and
ground-based optical observations of the hot, metal-rich white dwarf
GD 394. Extreme-ultraviolet (EUV) observations in 1992-1996 revealed a
1.15d periodicity with a 25 per cent amplitude, hypothesized to be due
to metals in a surface accretion spot. We obtained phase resolved
HST/Space Telescope Imaging Spectrograph high resolution
far-ultraviolet spectra of GD 394 that sample the entire period, along
with a large body of supplementary data. We find no evidence for an
accretion spot, with the flux, accretion rate, and radial velocity of
GD 394 constant over the observed time-scales at ultraviolet and
optical wavelengths. We speculate that the spot may have no longer
been present when our observations were obtained, or that the EUV
variability is being caused by an otherwise undetected evaporating
planet. The atmospheric parameters obtained from separate fits to
optical and ultraviolet spectra are inconsistent, as is found for
multiple hot white dwarfs. We also detect non-photospheric, high
ionisation absorption lines of multiple volatile elements, which could
be evidence for a hot plasma cocoon surrounding the white dwarf.
Description:
To test the accretion spot hypothesis, we obtained eight
far-ultraviolet (FUV) spectra of GD 394 using the Space Telescope
Imaging Spectrograph (STIS) onboard the Hubble Space Telescope
(HST/STIS). The observations were taken between 2015 August 20 and
2015 August 21, timed to fully sample the 1.15d period seen in the
EUV. The observations were taken with the FUV-MAMA detector in
TIME-TAG mode, using the E140M grating covering the wavelength range
1144-1710Å with an average resolution of λ/91700 per pixel.
Optical spectroscopy was obtained on 2009 May 23, 2009 May 23, and
2015 November 15 using the High Resolution Echelle Spectrometer
(HIRES) on the 10m W.M. Keck Telescope (Vogt et al.
1994SPIE.2198..362V 1994SPIE.2198..362V) under Program IDs A284Hr, A284Hb, and N116Hb. On
both nights 3x300s exposures were taken covering the wavelength range
3125-5997Å. On the first night an additional 3x300s exposures were
taken covering the wavelength range 4457-7655Å using the GG475
filter. All of the exposures used the C5 aperture.
Further optical spectroscopy of GD 394 was obtained using the
Intermediate dispersion Spectrograph and Imaging System (ISIS) on the
4.2m William Herschel Telescope (WHT) on 2007 August 6 and 2016 August
13. The 2007 observation used the R1200 grating to cover the
wavelength ranges 4520-5262Å and 8260-9014Å, with a total
exposure time of 2882s. The 2016 observations used the R600B+R
gratings covering 3056-5409Å and 5772-9088Å with a total
exposure time of 1800s.
In addition to the new observations described above, we utilized the
following archival data sets: GD 394 was observed by the Far
Ultraviolet Spectroscopic Explorer (FUSE) spacecraft on eight
occasions; Shipman et al. (1995AJ....109.1220S 1995AJ....109.1220S) used the Goddard High
Resolution Spectrograph (GHRS), one of the first-light instruments on
HST, to observe GD 394 on 1992 June 18; GD 394 was also observed
multiple times by the International Ultraviolet Explorer (IUE) and
finally we retrieved an optical spectrum obtained by Gianninas,
Bergeron & Ruiz (2011ApJ...743..138G 2011ApJ...743..138G) from the Montreal White Dwarf
Database (MWDD, Dufour et al. 2017ASPC..509....3D 2017ASPC..509....3D) covering the
wavelength range 3780-5280Å.
Objects:
----------------------------------------------------------
RA (2000) DE Designation(s)
----------------------------------------------------------
21 12 44.04 +50 06 17.9 GD 394 = WD 2111+498
----------------------------------------------------------
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
tablea1.dat 60 24 Summary of the spectroscopic observations of
GD 394
tableb1.dat 60 110 Observed photospheric metal absorption lines
detected in the FUSE, STIS, and HIRES spectra
tableb2.dat 47 5 High-ionization absorption lines suspected to be
circumstellar detected in the FUSE and STIS
spectra
tableb3.dat 57 22 ISM absorption lines detected in the FUSE,
STIS, and HIRES spectra
--------------------------------------------------------------------------------
Byte-by-byte Description of file: tablea1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 A10 "Y:M:D" Date Date of observation
12- 21 A10 --- Inst Telescope and instrument used for the
observation
23- 30 A8 "HH:MM:SS" Time Time of observation
32- 36 I5 s ExpTime Total exposure time
38- 40 F3.1 --- Phase ? Phase positions relative to the start of
the first observation (1)
42- 60 A19 0.1nm Wvlrange Wavelenght range (in Å)
--------------------------------------------------------------------------------
Note (1): For the STIS FUV observations we give the phase position relative to
the 1.15d period, with the start of the first observation defining
phase zero
--------------------------------------------------------------------------------
Byte-by-byte Description of file: tableb1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 5 A5 --- Inst Instrument used for the spectra (FUSE, STIS
or HIRES)
7- 16 A10 --- Line Detected metal absorption lines
18 A1 --- f_Line [?*] Flag on Line (1)
20- 27 F8.3 0.1nm Restwvl Rest wavelength of the detected line (2)
29- 36 F8.3 0.1nm Obswvl ? Observed wavelenght of the detected line
38- 42 F5.2 km/s Deltav ? Velocity variation
44- 49 F6.3 km/s e_Deltav ? Error on Deltav
51- 55 F5.1 10-4nm EW ? Equivalent width measured according to the
prescriptions found in Vollmann & Eversberg
(2006AN....327..862V 2006AN....327..862V)
57- 60 F4.1 10-4nm e_EW ? Error on EW
--------------------------------------------------------------------------------
Note (1): Flag as follows:
? = Uncertainty on the associated line
* = Blended with CIV 1550.77Å
Note (2): The rest wavelengths for lines detected in HIRES spectra use the air
value, all others use the vacuum value
--------------------------------------------------------------------------------
Byte-by-byte Description of file: tableb2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 A4 --- Inst Instrument used for the spectra (FUSE or STIS)
6- 8 A3 --- Line Detected metal absorption lines
10 A1 --- f_Line [*] Flag on Line (1)
12- 19 F8.3 0.1nm Restwvl Rest wavelength of the detected line
21- 27 F7.2 0.1nm Obswvl ? Observed wavelenght of the detected line
29- 32 F4.1 km/s Deltav ? Velocity variation
34- 37 F4.2 km/s e_Deltav ? Error on Deltav
39- 42 F4.1 10-4nm EW ? Equivalent width measured according to the
prescriptions found in Vollmann & Eversberg
(2006AN....327..862V 2006AN....327..862V)
44- 47 F4.1 10-4nm e_EW ? Error on EW
--------------------------------------------------------------------------------
Note (1): Flag as follows:
* = Blended with FeIII 1550.862Å
--------------------------------------------------------------------------------
Byte-by-byte Description of file: tableb3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 5 A5 --- Inst Instrument used for the spectra (FUSE, STIS
or HIRES)
7- 10 A4 --- Line Detected metal absorption lines
12 A1 --- u_Line [?] Uncertainty flag on Line
14- 22 F9.4 0.1nm Restwvl Rest wavelength of the detected line (1)
24- 30 F7.2 0.1nm Obswvl Observed wavelenght of the detected line
32- 37 F6.2 km/s Deltav ? Velocity variation
39- 44 F6.3 km/s e_Deltav ? Error on Deltav
46- 50 F5.1 10-4nm EW Equivalent width measured according to the
prescriptions found in Vollmann & Eversberg
(2006AN....327..862V 2006AN....327..862V)
52- 57 F6.3 10-4nm e_EW Error on EW
--------------------------------------------------------------------------------
Note (1): The rest wavelengths for lines detected in HIRES spectra use the air
value, all others use the vacuum value
--------------------------------------------------------------------------------
History:
From electronic version of the journal
(End) Ana Fiallos [CDS] 21-Jul-2022