Download PPT

Hot DO and DB White Dwarfs
From the Sloan Digital Sky Survey
James Liebert
University of Arizona
with
Jurek Krzesinski
Mt. Suhora Observatory, Krakow, Poland
Simon Hugelmeyer
and
Stefan Dreizler
Inst. f. Astrophysik,
Georg-August Universitaet Gottingen
HYDEF07 Tuebingen
Sloan Digital Sky Survey
2.5-meter
o
Catalog of 9,000+
White Dwarfs
o Most are Hot
DA,DB..
o Eisenstein et al.
2006
Apache Peak, near Sunspot, NM
Daniel Eisenstein -- Cosmologist and Cataloguer of 9,316 White Dwarfs
SDSS two color
Diagram
Solid curves
Hydrogen models
(log g = 9,8,7)
and a blackbody
Dashed curves
Helium models
DO and DB Stars
with no Balmer jump
hug blackbody curve
HYDEF07 Tuebingen
DA
50,000 K
25,000 K
17,000 K
12,000 K
8,000 K
Harris et al.
HYDEF07 Tuebingen
60,000 K
DO
48,000 K
28,000 K
DB
11,000 K
Harris et al.
HYDEF07 Tuebingen
DB-DO Stars:
1. The Mass Distribution
2. Filling the “DB Gap”
3. A preliminary luminosity function
of DO-DB white dwarfs
HYDEF07 Tuebingen
Liebert, Bergeron, Holberg
348 DA White Dwarfs
From the
Palomar Green Survey
Koester and Weidemann
(1979)
first showed
from fitting colors
that the mean mass
of DA white dwarfs
was near 0.6M
HYDEF07 Tuebingen
Eisenstein et al. 2006, ApJS, 167, 40
Ttemperature Index Subtype -- 50,400 / Teff -- easier than plotting Teff
HYDEF07 Tuebingen
A. Beauchamp
PhD dissertation
Univ. Montreal
DB white dwarfs
have same mean mass
as the DA’s
But very few low and
high mass outliers
HYDEF07 Tuebingen
3% (<0.5)
75% (0.5-0.8)
27%(>0.8)
DA Mass Distribution Corrected to Fixed Volume of Space
Search volume to mlim ~ R(wd)3 = (distance)3
Mysore, India 1985 -- HYDEF85
J. Liebert reports in talk on DB-DO stars:
Up to now, no non-DA with an analyzed spectrum
has a Teff between 30,000 and 45,000K
came to be called the “DB gap”
1990s come and go
More DB / DO stars analyzed from different samples
A. Beauchamp completes PhD thesis on DB star models, fits spectra
Still.. No DB / DO found between 30,000 and 45,000 K.
Then comes the Sloan Digital Sky Survey..
HYDEF07 Tuebingen
Model
Synthetic
Spectra
From
Detlev Koester
All lines He I
(of course)
HYDEF07 Tuebingen
Little change of
Spectra with Teff
From 18-20,000K
Till 38,000K
He II 4686Å
starts appearing
at 38,000K
(super S/N ratio)
or 40,000K
HYDEF07 Tuebingen
Some fits to
possible “DB gappers”
HYDEF07 Tuebingen
Open squares: from 6.5-m MMT spectra
Filled squares: SDSS spectra
SDSS Stars in our near
the “DB gap” region
30,000 - 45,000 K
Tphot estimated from
SDSS u g r I z mags
with an assumption
about extinction
Tspect from fitting
He I line spectrum
HYDEF07 Tuebingen
Ratio DA/non-DA
appears lower
above 50,000K
and below 20,000K
than inbetween
DB “gap”
HYDEF07 Tuebingen
DA LF overestimated for
Teff > 50,000K for
several reasons
------------------------------
-------------------PG incomplete
HYDEF07 Tuebingen