2,510 research outputs found
HD 49798: Its History of Binary Interaction and Future Evolution
The bright subdwarf-O star (sdO), HD 49798, is in a 1.55 day orbit with a
compact companion that is spinning at 13.2 seconds. Using the measurements of
the effective temperature (), surface gravity (), and
surface abundances of the sdO, we construct models to study the evolution of
this binary system using Modules for Experiments in Stellar Astrophysics
(). Previous studies of the compact companion have disagreed on
whether it is a white dwarf (WD) or a neutron star (NS). From the published
measurements of the companion's spin and spin-up rate, we agree with Mereghetti
and collaborators that a NS companion is more likely. However, since there
remains the possibility of a WD companion, we use our constructed
models to run simulations with both WD and NS companions that
help us constrain the past and future evolution of this system. If it presently
contains a NS, the immediate mass transfer evolution upon Roche lobe (RL)
filling will lead to mass transfer rates comparable to that implied in
ultraluminous X-ray sources (ULXs). Depending on the rate of angular momentum
extraction via a wind, the fate of this system is either a wide ( day) intermediate mass binary pulsar (IMPB) with a relatively
rapidly spinning NS ( s) and a high mass WD (), or a solitary millisecond pulsar (MSP).Comment: 6 pages, 4 figure
Quantitative spectroscopy of extreme helium stars - Model atmospheres and a non-LTE abundance analysis of BD+102179?
Extreme helium stars (EHe stars) are hydrogen-deficient supergiants of
spectral type A and B. They are believed to result from mergers in double
degenerate systems. In this paper we present a detailed quantitative non-LTE
spectral analysis for BD+102179, a prototype of this rare class of
stars, using UVES and FEROS spectra covering the range from 3100 to 10
000 {\AA}. Atmosphere model computations were improved in two ways. First,
since the UV metal line blanketing has a strong impact on the
temperature-density stratification, we used the Atlas12 code. Additionally, We
tested Atlas12 against the benchmark code Sterne3, and found only small
differences in the temperature and density stratifications, and good agreement
with the spectral energy distributions. Second, 12 chemical species were
treated in non-LTE. Pronounced non-LTE effects occur in individual spectral
lines but, for the majority, the effects are moderate to small. The
spectroscopic parameters give = 17 300300 K and
= 2.800.10, and an evolutionary mass of 0.550.05 . The star
is thus slightly hotter, more compact and less massive than found in previous
studies. The kinematic properties imply a thick-disk membership, which is
consistent with the metallicity Fe/H and -enhancement.
The refined light-element abundances are consistent with the white dwarf merger
scenario. We further discuss the observed helium spectrum in an appendix,
detecting dipole-allowed transitions from about 150 multiplets plus the most
comprehensive set of known/predicted isolated forbidden components to date.
Moreover, a so far unreported series of pronounced forbidden He I components is
detected in the optical-UV.Comment: Accepted for publication in MNRAS, 26 pages, 19 Figure
Detailed follow up studies of three ultracompact sdB binaries
We present follow-up studies of three ultracompact hot subdwarf binaries.
Using data from the Zwicky Transient Facility, we find orbital periods of 33.6,
37.3, and 36.9 minutes for ZTF 1946+3203, ZTF 0640+1738, and ZTF 0643+0318
respectively. The light curves show ellipsoidal variability of the hot subdwarf
star with potential eclipses of an accretion disc. Phase-resolved spectroscopic
observations with Keck were used to measure a radial velocity curve and
atmospheric parameters of the hot subdwarf stars. ZTF J0643 shows evidence of
accretion disc emission lines in the average spectrum. Combining light curve
and spectroscopic fits will allow us to measure precise system properties such
as masses, to determine the evolutionary history and future evolution of the
system.Comment: Accepted for publication in Bulletin de la Soci\'et\'e Royale des
Sciences de Li\`ege, proceedings for the sdOB10 conference, 10 pages, 1
figur
PSR J1024β0719: A Millisecond Pulsar in an Unusual Long-period Orbit
PSR J1024β0719 is a millisecond pulsar that was long thought to be isolated. However, puzzling results concerning its velocity, distance, and low rotational period derivative have led to a reexamination of its properties. We present updated radio timing observations along with new and archival optical data which show that PSR J1024β0719 is most likely in a long-period (2β20 kyr) binary system with a low-mass (β0.4 Mβ), low-metallicity (z β -0.9 dex) main-sequence star. Such a system can explain most of the anomalous properties of this pulsar. We suggest that this system formed through a dynamical exchange in a globular cluster that ejected it into a halo orbit, which is consistent with the low observed metallicity for the stellar companion. Further astrometric and radio timing observations such as measurement of the third period derivative could strongly constrain the range of orbital parameters
A novel method for transient detection in high-cadence optical surveys: Its application for a systematic search for novae in M31
[abridged] In large-scale time-domain surveys, the processing of data, from
procurement up to the detection of sources, is generally automated. One of the
main challenges is contamination by artifacts, especially in regions of strong
unresolved emission. We present a novel method for identifying candidates for
variables and transients from the outputs of such surveys' data pipelines. We
use the method to systematically search for novae in iPTF observations of the
bulge of M31. We demonstrate that most artifacts produced by the iPTF pipeline
form a locally uniform background of false detections approximately obeying
Poissonian statistics, whereas genuine variables and transients as well as
artifacts associated with bright stars result in clusters of detections, whose
spread is determined by the source localization accuracy. This makes the
problem analogous to source detection on images produced by X-ray telescopes,
enabling one to utilize tools developed in X-ray astronomy. In particular, we
use a wavelet-based source detection algorithm from the Chandra data analysis
package CIAO. Starting from ~2.5x10^5 raw detections made by the iPTF data
pipeline, we obtain ~4000 unique source candidates. Cross-matching these
candidates with the source-catalog of a deep reference image, we find
counterparts for ~90% of them. These are either artifacts due to imperfect PSF
matching or genuine variable sources. The remaining ~400 detections are
transient sources. We identify novae among these candidates by applying
selection cuts based on the expected properties of nova lightcurves. Thus, we
recovered all 12 known novae registered during the time span of the survey and
discovered three nova candidates. Our method is generic and can be applied for
mining any target out of the artifacts in optical time-domain data. As it is
fully automated, its incompleteness can be accurately computed and corrected
for.Comment: 16 pages, 8 figures, accepted to A&
Variability of Red Supergiants in M31 from the Palomar Transient Factory
Most massive stars end their lives as Red Supergiants (RSGs), a short-lived
evolution phase when they are known to pulsate with varying amplitudes. The RSG
period-luminosity (PL) relation has been measured in the Milky Way, the
Magellanic Clouds and M33 for about 120 stars in total. Using over 1500 epochs
of R-band monitoring from the Palomar Transient Factory (PTF) survey over a
five-year period, we study the variability of 255 spectroscopically cataloged
RSGs in M31. We find that all RGSs brighter than M_K~ -10 mag
(log(L/L_sun)>4.8) are variable at dm_R>0.05 mag. Our period analysis finds 63
with significant pulsation periods. Using the periods found and the known
values of M_K for these stars, we derive the RSG PL relation in M31 and show
that it is consistent with those derived earlier in other galaxies of different
metallicities. We also detect, for the first time, a sequence of likely
first-overtone pulsations. Comparison to stellar evolution models from MESA
confirms the first overtone hypothesis and indicates that the variable stars in
this sample have 12 M_sun<M<24 M_sun. As these RSGs are the immediate
progenitors to Type II-P core-collapse supernovae (SNe), we also explore the
implication of their variability in the initial-mass estimates for SN
progenitors based on archival images of the progenitors. We find that this
effect is small compared to the present measurement errors.Comment: 17 pages, 10 figure
Electromagnetic characterization of the LISA verification binary ZTF J05265934
We present an analysis of new and archival data to the 20.506-minute LISA
verification binary J052610.42593445.32 (J05265934). Our joint
spectroscopic and photometric analysis finds that the binary contains an unseen
CO-core white dwarf primary with an
post-core-burning subdwarf, or low-mass white
dwarf, companion. Given the short orbital period and relatively large total
binary mass, we find that LISA will detect this binary with signal-to-noise
ratio after 4 years of observations. J05265934 is expected to merge
within and likely result in a scenario Type
Ia supernova or form a He-rich star which will evolve into a massive single
white dwarf.Comment: 9 pages, 4 figures, 2 tables. Accepted in Ap
Modelling the AM CVn and Double Detonation Supernova Progenitor Binary System CD-3011223
We present a detailed modelling study of CD-3011223 (CD-30), a hot
subdwarf (sdB)-white dwarf (WD) binary identified as a double detonation
supernova progenitor, using the open-source stellar evolution software MESA. We
focus on implementing binary evolution models carefully tuned to match the
observed characteristics of the system including and .
For the first time, we account for the structure of the hydrogen envelope
throughout the modelling, and find that the inclusion of element diffusion is
important for matching the observed radius and temperature. We investigate the
two sdB mass solutions (0.47 and 0.54 ) previously proposed for this
system, strongly favouring the 0.47 solution. The WD cooling age is
compared against the sdB age using our models, which suggest an sdB likely
older than the WD, contrary to the standard assumption for compact sdB-WD
binaries. Subsequently, we propose a possible alternate formation channel for
CD-30. We also perform binary evolution modelling of the system to study
various aspects such as mass transfer, orbital period evolution and luminosity
evolution. Our models confirm CD-30 as a double detonation supernova
progenitor, expected to explode Myr from now. The WD accretes a
thick helium shell that causes a detonation, leaving
a 0.30 sdB ejected at 750 km/s. The final 15 Myr of the
system are characterised by helium accretion which dominates the system
luminosity, possibly resembling an AM CVn-type system.Comment: 12 pages, 8 figures. Accepted for publication in MNRA
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