113 research outputs found
A population synthesis study of the luminosity function of hot white dwarfs
Context. We present a coherent and detailed Monte Carlo simulation of the population of hot white dwarfs. We assess the statistical significance of the hot end of the white dwarf luminosity function and the role played by the bolometric corrections of hydrogen-rich white dwarfs at high effective temperatures. Aims. We use the most up-to-date stellar evolutionary models and implement a full description of the observational selection biases to obtain realistic simulations of the observed white dwarf population. Methods. Our theoretical results are compared with the luminosity function of hot white dwarfs obtained from the Sloan Digital Sky Survey (SDSS), for both DA and non-DA white dwarfs. Results. We find that the theoretical results are in excellent agreement with the observational data for the population of white dwarfs with hydrogen deficient atmospheres (non-DA white dwarfs). For the population of white dwarfs with hydrogen-rich atmospheres (white dwarfs of the DA class), our simulations show some discrepancies with the observations for the brightest luminosity bins, namely those corresponding to luminosities larger than ~10 L.These discrepancies can be attributed to the way in which the masses of the white dwarfs contributing to this luminosity bin have been computed, as most of them have masses smaller than the theoretical lower limit for carbon-oxygen white dwarfs. Conclusions. We conclude that the way in which the observational luminosity function of hot white dwarfs is obtained is very sensitive to the particular implementation of the method used to derive the masses of the sample. We also provide a revised luminosity function for hot white dwarfs with hydrogen-rich atmospheres. © ESO, 2014.Peer ReviewedPostprint (published version
No Neutron Star Companion To The Lowest Mass SDSS White Dwarf
SDSS J091709.55+463821.8 (hereafter J0917+4638) is the lowest surface gravity
white dwarf (WD) currently known, with log g = 5.55 +/- 0.05 (M ~ 0.17 M_sun;
Kilic et al. 2007a,b). Such low-mass white dwarfs (LMWDs) are believed to
originate in binaries that evolve into WD/WD or WD/neutron star (NS) systems.
An optical search for J0917+4638's companion showed that it must be a compact
object with a mass >= 0.28 M_sun (Kilic 2007b). Here we report on Green Bank
Telescope 820 MHz and XMM-Newton X-ray observations of J0917+4638 intended to
uncover a potential NS companion to the LMWD. No convincing pulsar signal is
detected in our radio data. Our X-ray observation also failed to detect X-ray
emission from J0917+4638's companion, while we would have detected any of the
millisecond radio pulsars in 47 Tuc. We conclude that the companion is almost
certainly another WD.Comment: 4 pages, 1 table; to appear in the Astrophysical Journal Letter
A Strategy for Finding Near Earth Objects with the SDSS Telescope
We present a detailed observational strategy for finding Near Earth Objects
(NEOs) with the Sloan Digital Sky Survey (SDSS) telescope. We investigate
strategies in normal, unbinned mode as well as binning the CCDs 2x2 or 3x3,
which affects the sky coverage rate and the limiting apparent magnitude. We
present results from 1 month, 3 year and 10 year simulations of such surveys.
For each cadence and binning mode, we evaluate the possibility of achieving the
Spaceguard goal of detecting 90% of 1 km NEOs (absolute magnitude H <= 18 for
an albedo of 0.1). We find that an unbinned survey is most effective at
detecting H <= 20 NEOs in our sample. However, a 3x3 binned survey reaches the
Spaceguard Goal after only seven years of operation. As the proposed large
survey telescopes (PanStarss; LSST) are at least 5-10 years from operation, an
SDSS NEO survey could make a significant contribution to the detection and
photometric characterization of the NEO population.Comment: Accepted by AJ -- 12 pages, 11 figure
SDSSJ103913.70+533029.7: A Super Star Cluster in the Outskirts of a Galaxy Merger
We describe the serendipitous discovery in the spectroscopic data of the
Sloan Digital Sky Survey of a star-like object, SDSSJ103913.70+533029.7, at a
heliocentric radial velocity of +1012 km/s. Its proximity in position and
velocity to the spiral galaxy NGC 3310 suggests an association with the galaxy.
At this distance, SDSSJ103913.70+533029.7 has the luminosity of a super star
cluster and a projected distance of 17 kpc from NGC 3310. Its spectroscopic and
photometric properties imply a mass of > 10^6 solar masses and an age close to
that of the tidal shells seen around NGC 3310, suggesting that it formed in the
event which formed the shells.Comment: Accepted by AJ: 4 figures (1 color
The Environment of Passive Spiral Galaxies in the SDSS
In previous work on galaxy clusters, several authors reported a discovery of
an unusual population of galaxies, which have spiral morphologies, but do not
show any star formation activity. These galaxies are called ``passive
spirals'', and have been interesting since it has been difficult to understand
the existence of such galaxies. Using a volume limited sample (0.05<z<0.1 and
Mr<-20.5; 25813 galaxies) of the Sloan Digital Sky Survey data, we have found
73 (0.280.03%) passive spiral galaxies and studied their environments. It
is found that passive spiral galaxies live in local galaxy density 1-2
Mpc and 1-10 cluster-centric virial radius. Thus the origins of passive
spiral galaxies are likely to be cluster related. These characteristic
environments coincide with the previously reported environment where galaxy
star formation rate suddenly declines and the so-called morphology-density
relation turns. It is likely that the same physical mechanism is responsible
for all of these observational results. The existence of passive spiral
galaxies suggests that a physical mechanism that works calmly is preferred to
dynamical origins such as major merger/interaction since such a mechanism can
destroy spiral arm structures. Compared with observed cluster galaxy evolution
such as the Butcher-Oemler effect and the morphological Butcher-Oemler effect,
passive spiral galaxies are likely to be a galaxy population in transition
between red, elliptical/S0 galaxies in low redshift clusters and blue, spiral
galaxies more numerous in higher redshift clusters.Comment: 31 pages, 13 figures, PASJ in pres
Sloan Digital Sky Survey Multicolor Observations of GRB010222
The discovery of an optical counterpart to GRB010222 (detected by BeppoSAX;
Piro 2001) was announced 4.4 hrs after the burst by Henden (2001a). The Sloan
Digital Sky Survey's 0.5m photometric telescope (PT) and 2.5m survey telescope
were used to observe the afterglow of GRB010222 starting 4.8 hours after the
GRB. The 0.5m PT observed the afterglow in five, 300 sec g' band exposures over
the course of half an hour, measuring a temporal decay rate in this short
period of F_nu \propto t^{-1.0+/-0.5}. The 2.5m camera imaged the counterpart
nearly simultaneously in five filters (u' g' r' i' z'), with r' = 18.74+/-0.02
at 12:10 UT. These multicolor observations, corrected for reddening and the
afterglow's temporal decay, are well fit by the power-law F_nu \propto
nu^{-0.90+/-0.03} with the exception of the u' band UV flux which is 20% below
this slope. We examine possible interpretations of this spectral shape,
including source extinction in a star forming region.Comment: 8 pages, 4 figures, accepted for publication in ApJ. Two figures
added, minor changes to text in this draft. Related material can be found at:
http://sdss.fnal.gov:8000/grb
Asteroseismological analysis of the polluted ZZ Ceti star G29-38 with TESS
G\,2938 (TIC~422526868) is one of the brightest () and closest (\,pc) pulsating white dwarfs with a hydrogen-rich atmosphere (DAV/ZZ
Ceti class). It was observed by the {\sl TESS} spacecraft in sectors 42 and 56.
The atmosphere of G~2938 is polluted by heavy elements that are expected to
sink out of visible layers on short timescales. The photometric {\sl TESS} data
set spans days in total, and from this, we identified 56 significant
pulsation frequencies, that include rotational frequency multiplets. In
addition, we identified 30 combination frequencies in each sector. The
oscillation frequencies that we found are associated with -mode pulsations,
with periods spanning from 260 s to 1400 s. We identified %three
distinct rotational frequency triplets with a mean separation of 4.67 Hz and a quintuplet with a mean separation of 6.67 Hz, from which we estimated a rotation period of
about days. We determined a constant period spacing of 41.20~s
for modes and 22.58\,s for modes. We performed
period-to-period fit analyses and found an asteroseismological model with
, K, and
(with a hydrogen envelope mass of ), in good agreement with the values derived from
spectroscopy. We obtained an asteroseismic distance of 17.54 pc, which is in
excellent agreement with that provided by {\sl Gaia} (17.51 pc).Comment: 17 pages, Accepted for publication in MNRA
- …