7,579 research outputs found
A search for variable white dwarfs in large area time domain surveys: a pilot study in SDSS Stripe 82
We present a method to reliably select variable white dwarfs from large area
time domain surveys and apply this method in a pilot study to search for
pulsating white dwarfs in the Sloan Digital Sky Survey Stripe 82. From a sample
400 high-confidence white dwarf candidates, we identify 24 which show
significant variability in their multi-epoch Stripe 82 data. Using colours, we
further selected a sample of pulsating white dwarf (ZZ Ceti) candidates and
obtained high cadence follow up for six targets. We confirm five of our
candidates as cool ZZ Cetis, three of which are new discoveries. Among our 24
candidates we also identify: one eclipsing binary, two magnetic white dwarfs
and one pulsating PG1159 star. Finally we discuss the possible causes for the
variability detected in the remaining targets. Even with sparse multi-epoch
data over the limited area of Stripe 82, we demonstrate that our selection
method can successfully identify various types of variable white dwarfs and
efficiently select high-confidence ZZ Ceti candidates.Comment: Accepted for publication in MNRAS, 14 pages, 11 figure
The population of hot subdwarf stars studied with Gaia II. The Gaia DR2 catalogue of hot subluminous stars
Based on data from the ESA Gaia Data Release 2 (DR2) and several
ground-based, multi-band photometry surveys we compiled an all-sky catalogue of
hot subluminous star candidates selected in Gaia DR2 by means of
colour, absolute magnitude and reduced proper motion cuts. We expect the
majority of the candidates to be hot subdwarf stars of spectral type B and O,
followed by blue horizontal branch stars of late B-type (HBB), hot post-AGB
stars, and central stars of planetary nebulae. The contamination by cooler
stars should be about . The catalogue is magnitude limited to Gaia
and covers the whole sky. Except within the Galactic plane
and LMC/SMC regions, we expect the catalogue to be almost complete up to about
. The main purpose of this catalogue is to serve as input
target list for the large-scale photometric and spectroscopic surveys which are
ongoing or scheduled to start in the coming years. In the long run, securing a
statistically significant sample of spectroscopically confirmed hot subluminous
stars is key to advance towards a more detailed understanding of the latest
stages of stellar evolution for single and binary stars.Comment: 13 pages, A&A, accepte
Analysis of cool DO-type white dwarfs from the Sloan Digital Sky Survey Data Release 10
We report on the identification of 22 new cool DO-type white dwarfs (WD)
detected in Data Release 10 (DR10) of the Sloan Digital Sky Survey (SDSS).
Among them, we found one more member of the so-called hot-wind DO WDs, which
show ultrahigh excitation absorption lines. Our non-LTE model atmosphere
analyses of these objects and two not previously analyzed hot-wind DO WDs,
revealed effective temperatures and gravities in the ranges Teff=45-80kK and
log g= 7.50-8.75. In eight of the spectra we found traces of C (0.001-0.01, by
mass). Two of these are the coolest DO WDs ever discovered that still show a
considerable amount of C in their atmospheres. This is in strong contradiction
with diffusion calculations, and probably, similar to what is proposed for DB
WDs, a weak mass-loss is present in DO WDs. One object is the most massive DO
WD discovered so far with a mass of 1.07 M_sun if it is an ONe-WD or 1.09 M_sun
if it is a CO-WD. We furthermore present the mass distribution of all known hot
non-DA (pre-) WDs and derive the hot DA to non-DA ratio for the SDSS DR7
spectroscopic sample. The mass distribution of DO WDs beyond the wind limit
strongly deviates from the mass distribution of the objects before the wind
limit. We address this phenomenon by applying different evolutionary input
channels. We argue that the DO WD channel may be fed by about 13% by
post-extreme-horizontal branch stars and that PG1159 stars and O(He) stars may
contribute in a similar extent to the non-DA WD channel.Comment: 13 pages, accepted for publication in A&
Breakdown of Angular Momentum Selection Rules in High Pressure Optical Pumping Experiments
We present measurements, using two complementary methods, of the breakdown of
atomic angular momentum selection rules in He-broadened Rb vapor. Atomic dark
states are rendered weakly absorbing due to fine-structure mixing during Rb-He
collisions. The effect substantially increases the photon demand for optical
pumping of dense vapors
Remarks on the properties of elliptical galaxies in modified Newtonian dynamics
Two incorrect arguments against MOND in elliptical galaxies could be that the
equivalent circular velocity curves tend to become flat at much larger
accelerations than in spiral galaxies, and that the Newtonian dark matter halos
are more concentrated than in spirals. Here, we compare published scaling
relations for the dark halos of elliptical galaxies to the scaling relations
expected for MONDian phantom halos. We represent the baryonic content of
galaxies by spherical profiles, and their corresponding MONDian phantom halos
by logarithmic halos. We then derive the surface densities, central densities,
and phase space densities and compare them with published scaling relations. We
conclude that it is possible to get flat circular velocity curves at high
acceleration in MOND, and that this happens for baryonic distributions
described by Jaffe profiles in the region where the circular velocity curve is
flat. Moreover, the scaling relations of dark halos of ellipticals are
remarkably similar to the scaling relations of phantom halos of MOND.Comment: Accepted for publication in A and
Search for Lepton Flavor-Violating "tau -> mu gamma" decay
We search for the lepton flavor-violating "tau -> mu gamma" decay using 29.7
million tau pairs accumulated by the Belle experiment. The main background
sources are found to be tau pairs with "tau -> mu nu nu" decay and radiative
dimuon events. One event is observed in the signal region, while 2.5 +- 0.6
background events are expected. A preliminary upper limit Br(tau -> mu gamma) <
6 x 10^{-7} at the 90% confidence limit is obtained.Comment: Invited talk at the Seventh International Workshop on Tau Lepton
Physics (TAU02), Santa Cruz, Ca, USA, Sept 2002, 6 pages, LaTeX, 13 eps
figure
Precision Measurement of the n-3He Incoherent Scattering Length Using Neutron Interferometry
We report the first measurement of the low-energy neutron-He incoherent
scattering length using neutron interferometry: fm. This is in good agreement with a
recent calculation using the AV18+3N potential. The neutron-He scattering
lengths are important for testing and developing nuclear potential models that
include three nucleon forces, effective field theories for few-body nuclear
systems, and neutron scattering measurements of quantum excitations in liquid
helium. This work demonstrates the first use of a polarized nuclear target in a
neutron interferometer.Comment: 4 figure
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