152 research outputs found
RNO 54: A Previously Unappreciated FU Ori Star
We present evidence in support of the hypothesis that the young stellar object RNO 54 is a mature-stage FU Ori type source. The star was first cataloged as a "red nebulous object" in the 1980s but appears to have undergone its outburst prior to the 1890s. Present-day optical and near-infrared spectra are consistent with those of other FU Ori-type stars, both in the details of spectral line presence and shape, and in the overall change in spectral type from an FGK-type in the optical, to the M-type presented in the near-infrared. In addition, the spectral energy distribution of RNO 54 is well-fit by a pure-accretion disk model with parameters: M = 10-3.45±0.06 M⊙ yr−1, M* = 0.23 ± 0.06 M⊙, and Rinner = 3.68 ± 0.76 R⊙, though we believe Rinner is likely close to its upper range of 4.5R⊙ in order to produce a Tmax = 7000K that is consistent with the optical to near-infrared spectra. The resulting Lacc is ∼265 L⊙. To find these values, we adopted a source distance d = 1400 pc and extinction AV = 3.9 mag, along with disk inclination i = 50 deg based on the consideration of confidence intervals from our initial disk model, and in agreement with observational constraints. The new appreciation of a well-known source as an FU Ori-type object suggests that other such examples may be lurking in extant samples
Discovery of 36 eclipsing EL CVn binaries found by the Palomar Transient Factory
We report the discovery and analysis of 36 new eclipsing EL CVn-type
binaries, consisting of a core helium-composition pre-white dwarf and an
early-type main-sequence companion, more than doubling the known population of
these systems. We have used supervised machine learning methods to search 0.8
million lightcurves from the Palomar Transient Factory, combined with SDSS,
Pan-STARRS and 2MASS colours. The new systems range in orbital periods from
0.46-3.8 d and in apparent brightness from ~14-16 mag in the PTF or
filters. For twelve of the systems, we obtained radial velocity
curves with the Intermediate Dispersion Spectrograph at the Isaac Newton
Telescope. We modelled the lightcurves, radial velocity curves and spectral
energy distributions to determine the system parameters. The radii (0.3-0.7
) and effective temperatures (8000-17000 K) of the
pre-He-WDs are consistent with stellar evolution models, but the masses
(0.12-0.28 ) show more variance than models predicted. This
study shows that using machine learning techniques on large synoptic survey
data is a powerful way to discover substantial samples of binary systems in
short-lived evolutionary stages
The OmegaWhite Survey for Short-Period Variable Stars IV: Discovery of the warm DQ white dwarf OW J175358.85-310728.9
We present the discovery and follow-up observations of the second known
variable warm DQ white dwarf OW J175358.85-310728.9 (OW J1753-3107). OW
J1753-3107 is the brightest of any of the currently known warm or hot DQ and
was discovered in the OmegaWhite Survey as exhibiting optical variations on a
period of 35.5452 (2) mins, with no evidence for other periods in its light
curves. This period has remained constant over the last two years and a
single-period sinusoidal model provides a good fit for all follow-up light
curves. The spectrum consists of a very blue continuum with strong absorption
lines of neutral and ionised carbon, a broad He I 4471 A line, and possibly
weaker hydrogen lines. The C I lines are Zeeman split, and indicate the
presence of a strong magnetic field. Using spectral Paschen-Back model
descriptions, we determine that OW J1753-3107 exhibits the following physical
parameters: T_eff = 15430 K, log(g) = 9.0, log(N(C)/N(He)) = -1.2, and the mean
magnetic field strength is B_z =2.1 MG. This relatively low temperature and
carbon abundance (compared to the expected properties of hot DQs) is similar to
that seen in the other warm DQ SDSS J1036+6522. Although OW J1753-3107 appears
to be a twin of SDSS J1036+6522, it exhibits a modulation on a period slightly
longer than the dominant period in SDSS J1036+6522 and has a higher carbon
abundance. The source of variations is uncertain, but they are believed to
originate from the rotation of the magnetic white dwarf.Comment: 11 pages, 8 figures, 7 tables. Accepted for publication by MNRA
An Extremely Massive White Dwarf Escaped from the Hyades Star Cluster
We searched the Gaia DR3 database for ultramassive white dwarfs with kinematics consistent with having escaped the nearby Hyades open cluster, identifying three such candidates. Two of these candidates have masses estimated from Gaia photometry of approximately 1.1 solar masses; their status as products of single-stellar evolution that have escaped the cluster was deemed too questionable for immediate follow-up analysis. The remaining candidate has an expected mass >1.3 solar masses, significantly reducing the probability of it being an interloper. Analysis of follow-up Gemini GMOS spectroscopy for this source reveals a nonmagnetized hydrogen atmosphere white dwarf with a mass and age consistent with having formed from a single star. Assuming a single-stellar-evolution formation channel, we estimate a 97.8% chance that the candidate is a true escapee from the Hyades. With a determined mass of 1.317 solar masses, this is potentially the most massive known single-evolution white dwarf and is by far the most massive with a strong association with an open cluster
PTF1 J085713+331843, a new post common-envelope binary in the orbital period gap of cataclysmic variables
We report the discovery and analysis of PTF1 J085713+331843, a new eclipsing post common-envelope detached white-dwarf red-dwarf binary with a 2.5h orbital period discovered by the Palomar Transient Factory. ULTRACAM multicolour photometry over multiple orbital periods reveals a light curve with a deep flat-bottomed primary eclipse and a strong reflection effect. Phase-resolved spectroscopy shows broad Balmer absorption lines from the DA white dwarf and phase-dependent Balmer emission lines originating on the irradiated side of the red dwarf. The temperature of the DA white dwarf is K and the spectral type of the red dwarf is M3-5. A combined modelling of the light curve and the radial velocity variations results in a white dwarf mass of and radius of , and a red dwarf mass and radius of and . The system is either a detached cataclysmic variable or has emerged like from the common envelope phase at nearly its current orbital period. In Myr, this system will become a cataclysmic variable in the period gap
Strongly magnetized accretion in two ultracompact binary systems
We present the discoveries of two of AM CVn systems, Gaia14aae and
SDSS~J080449.49+161624.8, which show X-ray pulsations at their orbital periods,
indicative of magnetically collimated accretion. Both also show indications of
higher rates of mass transfer relative to the expectations from binary
evolution driven purely by gravitational radiation, based on existing optical
data for Gaia14aae, which show a hotter white dwarf temperature than expected
from standard evolutionary models, and X-ray data for SDSS~J080449.49+161624.8
which show a luminosity 10-100 times higher than those for other AM~CVn at
similar orbital periods. The higher mass transfer rates could be driven by
magnetic braking from the disk wind interacting with the magnetosphere of the
tidally locked accretor. We discuss implications of this additional angular
momentum transport mechanism for evolution and gravitational wave detectability
of AM CVn objects.Comment: 5 pages, 3 figures, accepted to MNRAS Letter
Strongly magnetized accretion in ultracompact binary systems
AM CVn systems are binary star systems with orbital periods less than 70 minutes in which a white dwarf accretes matter from a companion star, which must be either a stripped helium burning star, or a white dwarf of lower mass than the accretor. Here, we present the discoveries of two of these systems in which there is mass transfer from the lighter white dwarf or helium star onto a strongly magnetized heavier white dwarf. These represent the first clear example of magnetized accretion in ultracompact binaries. These systems, along with similar systems that are slightly more widely separated, and that have not started to transfer mass yet, are expected to be the primary source of gravitational waves to be detected by space-based gravitational wave observatories. The presence of strong magnetic fields can substantially affect both the evolution of the binaries, and also the particular wave forms of the gravitational waves themselves, and understanding these magnetic effects is vital for understanding what to expect from the Laser Interferometer Space Antenna
Zwicky Transient Facility constraints on the optical emission from the nearby repeating FRB 180916.J0158+65
The discovery rate of fast radio bursts (FRBs) is increasing dramatically
thanks to new radio facilities. Meanwhile, wide-field instruments such as the
47 deg Zwicky Transient Facility (ZTF) survey the optical sky to study
transient and variable sources. We present serendipitous ZTF observations of
the CHIME repeating source FRB 180916.J0158+65, that was localized to a spiral
galaxy 149 Mpc away and is the first FRB suggesting periodic modulation in its
activity. While 147 ZTF exposures corresponded to expected high-activity
periods of this FRB, no single ZTF exposure was at the same time as a CHIME
detection. No optical source was found at the FRB location in 683
ZTF exposures, totalling 5.69 hours of integration time. We combined ZTF upper
limits and expected repetitions from FRB 180916.J0158+65 in a statistical
framework using a Weibull distribution, agnostic of periodic modulation priors.
The analysis yielded a constraint on the ratio between the optical and radio
fluences of , corresponding to an optical energy erg for a fiducial 10 Jy ms FRB (90%
confidence). A deeper (but less statistically robust) constraint of can be placed assuming a rate of Jy ms)= hr and
FRB occurring during exposures taken in high-activity windows. The
constraint can be improved with shorter per-image exposures and longer
integration time, or observing FRBs at higher Galactic latitudes. This work
demonstrated how current surveys can statistically constrain multi-wavelength
counterparts to FRBs even without deliberately scheduled simultaneous radio
observation.Comment: Accepted for publication in ApJL, 9 pages, 4 figures, 1 tabl
Phase-Resolved Spectroscopy of Gaia14aae: Line Emission From Near the White Dwarf Surface
AM CVn binaries are a class of ultracompact, hydrogen-deficient binaries,
each consisting of a white dwarf accreting helium-dominated material from a
degenerate or semi-degenerate donor star. Of the 56 known systems, only
Gaia14aae undergoes complete eclipses of its central white dwarf, allowing the
parameters of its stellar components to be tightly constrained. Here, we
present phase-resolved optical spectroscopy of Gaia14aae. We use the spectra to
test the assumption that the narrow emission feature known as the `central
spike' traces the motion of the central white dwarf. We measure a central spike
velocity amplitude of km/s, which agrees at the 1 level
with the predicted value of km/s based on eclipse-derived system
parameters. The orbital phase offset of the central spike from its expected
position is , consistent with 0 . Doppler maps of
the He I lines in Gaia14aae show two accretion disc bright spots, as seen in
many AM CVn systems. The formation mechanism for the second spot remains
unclear. We detect no hydrogen in the system, but we estimate a 3
limit on H emission with an equivalent width of -1.14 \AA. Our
detection of nitrogen and oxygen with no corresponding detection of carbon, in
conjunction with evidence from recent studies, mildly favours a formation
channel in which Gaia14aae is descended from a cataclysmic variable with a
significantly evolved donor.Comment: 16 pages, accepted by MNRA
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