13 research outputs found
ST/STIS Spectroscopy of the White Dwarfs in the Short-Period Dwarf Novae LL And and EF Peg
We present new HST/STIS observations of the short-period dwarf novae LL And
and EF Peg during deep quiescence. We fit stellar models to the UV spectra and
use optical and IR observations to determine the physical parameters of the
whitedwarfs in the systems, the distances to the binaries, and the properties
of thesecondary stars. Both white dwarfs are relatively cool, having T_{eff}
near 15000K, and consistent with a mass of 0.6 M-sun. The white dwarf in LL And
appears to be of solar abundance or slightly lower while that in EF Peg is near
0.1-0.3 solar. LL And is found to be 760 pc away while EF Peg is closer at 380
pc. EF Peg appears to have an ~M5V secondary star, consistent with that
expected for its orbital period, while the secondary object in LL And remains a
mystery.Comment: Accepted in Ap
Measuring the Boundary Layer and Inner Accretion Disk Temperatures for WX Ceti During Superoutburst
We obtained EUV photometry, optical spectroscopy, and multi-color optical
photometry for WX Cet during its 1998 November superoutburst. WX Cet is only
the second short-period, low mass transfer CV (TOAD) to ever be observed in the
EUV. Our determined superhump period is consistent with that found by Kato et
al. (0.059 d) and we confirm that superhumps are grey in the optical. The
optical spectra provide direct evidence that the line emission region is
optically thick and our multi-wavelength photometric measurements are used to
determine the inner accretion disk and boundary layer temperatures during
superoutburst. Using a determined distance to WX Cet of ~130 pc, we find
T= 21,000K and T_{BL}~72,500K. Both values are in good agreement with
that expected by models of the superoutburst continuum being produced by the
inner disk and boundary layer.Comment: Accepted in PASP - July 2002 issu
Parallax and Distance Estimates for Fourteen Cataclysmic Variable Stars
I used the 2.4 m Hiltner telescope at MDM Observatory in an attempt to
measure trigonometric parallaxes for 14 cataclysmic variable stars. Techniques
are described in detail. In the best cases the parallax uncertainties are below
1 mas, and significant parallaxes are found for most of the program stars. A
Bayesian method which combines the parallaxes together with proper motions and
absolute magnitude constraints is developed and used to derive distance
estimates and confidence intervals. The most precise distance derived here is
for WZ Sge, for which I find 43.3 (+1.6, -1.5) pc. Six Luyten Half-Second stars
with previous precise parallax measurements were re-measured to test the
techniques, and good agreement is found.Comment: 33 pages, 3 figures. Astronomical Journal, accepte
Spitzer Observations of Var Her 04: Possible Detection of Dust Formation in a Super-Outbursting TOAD
We present four MIPS (24 \micron) and two IRAC (3.6, 4.5, 5.8, and 8.0
\micron) Spitzer observations of the newly discovered Tremendous Outburst
Amplitude Dwarf nova (TOAD) Var Her 04 during decline from super-outburst. The
four MIPS observations span 271 days and the two IRAC observations span 211
days. Along the line-of-sight to Var Her 04, there is a foreground M-star
within 1\arcsec of the variable; as a result, all of the Spitzer photometry
presented in this paper is a blend of the foreground M-star and Var Her 04. We
estimate the quiescent level of the TOAD to be magnitudes below
that of the M-star. Based upon the spectral energy distribution and the 2MASS
colors, we find the M-star to be an M3.5V dwarf at a distance of 80-130 pc.
Based upon its outburst amplitude and quiescent apparent magnitude, we estimate
the distance to Var Her 04 to be 200-400 pc, suggesting that the line-of-sight
foreground star is physically unrelated to the cataclysmic variable. All of the
Spitzer photometry is consistent with the photospheric emission of the
line-of-sight M3.5V star, except for one 24 \micron observation obtained after
the variable re-brightened. This 24 \micron flux density is 75 Jy
() above the preceding and following MIPS observations. We tentatively
suggest that the mid-infrared brightening of 75 Jy may be associated with
a dust formation event in the super-outburst ejecta. Assuming a dust
temperature of 100-400 K, we have estimated the amount of dust required. We
find M of dust is needed, consistent with amounts
of mass ejection in TOADs expected during super-outburst, and possibly making
TOADs important contributors to the recycling of the interstellar medium.Comment: Accepted for publication in The Astronomical Journa
HST/ACS Imaging of Omega Centauri: Optical Counterpart for the Quiescent Low-Mass X-Ray Binary
We report the discovery of an optical counterpart to a quiescent neutron star
in the globular cluster Omega Centauri (NGC 5139). The star was found as part
of our wide-field imaging study of Omega Cen using the Advanced Camera for
Surveys (ACS) on Hubble Space Telescope. Its magnitude and color (R_625 = 25.2,
B_435 - R_625 = 1.5) place it more than 1.5 magnitudes to the blue side of the
main sequence. Through an H-alpha filter it is ~ 1.3 magnitudes brighter than
cluster stars of comparable M_625 magnitude. The blue color and H-alpha excess
suggest the presence of an accretion disk, implying that the neutron star is
accreting from a binary companion and is thus a quiescent low-mass X-ray
binary. If the companion is a main-sequence star, then the faint absolute
magnitude (M_625 ~ 11.6) constrains it to be of very low mass (M <~ 0.14
Msolar). The faintness of the disk (M_435 ~ 13) suggests a very low rate of
accretion onto the neutron star. We also detect 13 probable white dwarfs and
three possible BY Draconis stars in the 20" x 20" region analyzed here,
suggesting that a large number of white dwarfs and active binaries will be
observable in the full ACS study.Comment: Accepted for Publication in the Astrophysical Journal. 5 pages, 4
figures, 1 table, uses emulateapj.sty. Figures 1 and 3 at reduced resolution.
New version contains revised magnitude calibration
Infrared Properties of Cataclysmic Variables from 2MASS: Results from the 2nd Incremental Data Release
Because accretion-generated luminosity dominates the radiated energy of most
cataclysmic variables, they have been ``traditionally'' observed primarily at
short wavelengths. Infrared observations of cataclysmic variables contribute to
the understanding of key system components that are expected to radiate at
these wavelengths, such as the cool outer disk, accretion stream, and secondary
star. We have compiled the J, H, and Ks photometry of all cataclysmic variables
located in the sky coverage of the 2 Micron All Sky Survey (2MASS) 2nd
Incremental Data Release. This data comprises 251 systems with reliably
identified near-IR counterparts and S/N > 10 photometry in one or more of the
three near-IR bands.Comment: 2 pages, including 1 figure. To appear in the proceedings of The
Physics of Cataclysmic Variables and Related Objects, Goettingen, Germany.
For our followup ApJ paper (in press), also see
http://www.ctio.noao.edu/~hoard/research/2mass/index.htm
The Dwarf Novae During Quiescence
We present a synthetic spectral analysis of nearly the entire FUV IUE archive
of spectra of DNe in or near quiescence. We have examined all of the systems
for which S/N permitted an analysis. The study includes 53 systems of all DN
subtypes both above and below the period gap. The spectra were uniformly
analyzed using synthetic spectral codes for optically thick accretion disks and
stellar photospheres along with the best-available distance measurements or
estimates. We present newly determined approximate WD temperatures or upper
limits and estimated accretion rates. The average temperature of WDs in DNe
below the period gap is ~18,000K. For WDs in DNe above the period gap, the
average WD temperature is ~26,000K. There is a flux component, in addition to a
WD photosphere, which contributes >60% of the flux in the FUV in 53% of the
quiescent DNe in this study. We find that for 41% of the DNe in our sample, a
WD photosphere provides >60% of the FUV flux. Accretion rates estimated from
the FUV alone for the sample of DNe during quiescence ranged from 10^-12
Msun/yr to 10^-10 Msun/yr.The additional flux component is almost certainly not
an optically thick accretion disk since, according to the disk instability
model, the disk should be optically thin and too cool during DN quiescence to
be a significant FUV continuum emitter. Among the candidates for the second
component of FUV light are the quiescent inner disk, a hot equatorial accretion
belt, and a hot rotating ring. The implications of our study for disk accretion
physics and CV evolution are discussed.Comment: 36 pages, 3 tables, 8 figures, final accepted version of manuscrip
Interferometric Astrometry with Hubble Space Telescope Fine Guidance Sensor 3:The Parallax of the Cataclysmic Variable TV Columbae
TV Columbae (TV Col) is a 13th magnitude Intermediate Polar (IP) Cataclysmic
Variable (CV), with multiple periods found in the light curves. Past estimates
predicted a distance of 400 parsec to greater than 500 parsec. Recently
completed Hubble Space Telescope (HST) Fine Guidance Sensor (FGS)
interferometric observations allow us to determine the first trigonometric
parallax to TV Col. This determination puts the distance of TV Col at 368
-15+17 parsecs.
CD-32 2376, a 10th magnitude Tycho Catalog star, is a reference star in the
TV Col frame. We find a distance of $127.7 -1+1 parsecs.Comment: 24 pages, 2 figure