110 research outputs found
The mass and radius of the M-dwarf in the short period eclipsing binary RR Caeli
We present new photometry and spectroscopy of the eclipsing white dwarf -
M-dwarf binary star RR Cae. We use timings of the primary eclipse from
white-light photo-electric photometry to derive a new ephemeris for the
eclipses. We find no evidence for any period change greater than Pdot/P ~ 5E-12
over a timescale of 10 years. We have measured the effective temperature of the
white dwarf, T_WD, from an analysis of two high resolution spectra of RR Cae
and find T_WD = (7540 +- 175)K. We estimate a spectral type of M4 for the
companion from the same spectra. We have combined new spectroscopic orbits for
the white dwarf and M-dwarf with an analysis of the primary eclipse and cooling
models for helium white dwarfs to measure the mass and radius of the M-dwarf.
The mass of the M-dwarf is (0.182 - 0.183) +- 0.013 Msun and the radius is
(0.203 - 0.215) +- 0.013 Rsun, where the ranges quoted for these values reflect
the range of white dwarf models used. In contrast to previous studies, which
lacked a spectroscopic orbit for the white dwarf, we find that the mass and
radius of the M-dwarf are normal for an M4 dwarf. The mass of the white dwarf
is (0.440 +-0.022) Msun. With these revised masses and radii we find that RR
Cae will become a cataclysmic variable star when the orbital period is reduced
from its current value of 7.3 hours to 121 minutes by magnetic braking in 9-20
Gyr. We note that there is night-to-night variability of a few seconds in the
timing of primary eclipse caused by changes to the shape of the primary
eclipse. We speculate as to the possible causes of this phenomenon. (Abridged)Comment: Accepted for publication in MNRAS. The paper contains 10 figures and
3 table
The mass and radius of the M dwarf companion to GD 448
We present spectroscopy and photometry of GD 448, a detached white dwarf - M dwarf binary with a period of 2.47 h. We find that the Na I 8200-Ă
feature is composed of narrow emission lines, owing to irradiation of the M dwarf by the white dwarf, within broad absorption lines that are essentially unaffected by heating. Combined with an improved spectroscopic orbit and gravitational redshift measurement from spectra of the Hα line, we are able to derive masses for the white dwarf and M dwarf directly (0.41 ± 0.01 and 0.096 ± 0.004 Mâ, respectively). We use a simple model of the Ca II emission lines to establish the radius of the M dwarf assuming the emission from its surface to be proportional to the incident flux per unit area from the white dwarf. The radius derived is 0.125 ± 0.020 Râ. The M dwarf appears to be a normal main-sequence star in terms of its mass and radius, and is less than half the size of its Roche lobe. The thermal time-scale of the M dwarf is much longer than the cooling age of the white dwarf, so we conclude that the M dwarf was unaffected by the common-envelope phase. The anomalous width of the Hα emission from the M dwarf remains to be explained, but the strength of the line may be due to X-ray heating of the M dwarf owing to accretion on to the white dwarf from the M dwarf wind
WASP 1628+10-an EL CVn-type binary with a very low mass stripped red giant star and multiperiodic pulsations
The star 1SWASP J162842.31+101416.7 (WASP 1628+10) is one of several EL CVn-type
stars recently identified using the Wide Angle Search for Planets (WASP) data base, i.e. an
eclipsing binary star in which an A-type dwarf star (WASP 1628+10 A) eclipses the remnant
of a disrupted red giant star (WASP 1628+10 B). We have measured the masses, radii and
luminosities of the stars in WASP 1628+10 using photometry obtained in three bands (u
,
g
, r
) with the ULTRACAM instrument and medium-resolution spectroscopy. The properties
of the remnant are well matched by models for stars in a rarely observed state evolving to
higher effective temperatures at nearly constant luminosity prior to becoming a very low mass
white dwarf composed almost entirely of helium, i.e. we confirm that WASP 1628+10 B
is a precursor of a helium white dwarf (pre-He-WD). WASP 1628+10 A appears to be a
normal A2 V star with a mass of 1.36 ± 0.05 M. By fitting models to the spectrum of this
star around the Hγ line we find that it has an effective temperature Teff, A = 7500 ± 200 K
and a metallicity [Fe/H] = â0.3 ± 0.3. The mass of WASP 1628+10 B is only 0.135 ±
0.02 M. The effective temperature of this pre-He-WD is approximately 9200 K. The ULTRACAM
photometry of WASP 1628+10 shows variability at several frequencies around
40 cycles dâ1, which is typical for ÎŽ Sct-type pulsations often observed in early A-type stars
like WASP 1628+10 A. We also observe frequencies near 114 and 129 cycles dâ1, much
higher than the frequencies normally seen in ÎŽ Sct stars. Additional photometry through the
primary eclipse will be required to confirm that these higher frequencies are due to pulsations
in WASP 1628+10 B. If confirmed, this would be only the second known example of a
pre-He-WD showing high-frequency pulsations
The population of white dwarf binaries with hot subdwarf companions
Hot subdwarfs (sdBs) are core helium-burning stars, which lost almost their
entire hydrogen envelope in the red-giant phase. Since a high fraction of those
stars are in close binary systems, common envelope ejection is an important
formation channel. We identified a total population of 51 close sdB+WD binaries
based on time-resolved spectroscopy and multi-band photometry, derive the WD
mass distribution and constrain the future evolution of these systems. Most WDs
in those binaries have masses significantly below the average mass of single
WDs and a high fraction of them might therefore have helium cores. We found 12
systems that will merge in less than a Hubble time and evolve to become either
massive C/O WDs, AM\,CVn systems, RCrB stars or even explode as supernovae type
Ia.Comment: 5 pages, 2 figures, to appear in the proceedings of the 19th European
White Dwarf Workshop, ASP Conf. Se
Dynamical constraints on some orbital and physical properties of the WD0137-349 A/B binary system
In this paper I deal with the WD0137-349 binary system consisting of a white
dwarf (WD) and a brown dwarf (BD) in a close circular orbit of about 116 min.
I, first, constrain the admissible range of values for the inclination i by
noting that, from looking for deviations from the third Kepler law, the
quadrupole mass moment Q would assume unlikely large values, incompatible with
zero at more than 1-sigma level for i 43 deg. Then, by
conservatively assuming that the most likely values for i are those that
prevent such an anomalous behavior of Q, i.e. those for which the third Kepler
law is an adequate modeling of the orbital period, I obtain i=39 +/- 2 deg.
Such a result is incompatible with the value i=35 deg quoted in literature by
more than 2 sigma. Conversely, it is shown that the white dwarf's mass range
obtained from spectroscopic measurements is compatible with my experimental
range, but not for i=35 deg. As a consequence, my estimate of yields an
orbital separation of a=(0.59 +/- 0.05)R_Sun and an equilibrium temperature of
BD of T_eq=(2087 +/- 154)K which differ by 10% and 4%, respectively, from the
corresponding values for i=35 deg.Comment: LaTex2e, 11 pages, 3 figures, no tables. It refers to gr-qc/0611126
and better clarify the result obtained there. Accepted by Astrophysics and
Space Scienc
Stellar adiabatic mass loss model and applications
Roche-lobe overflow and common envelope evolution are very important in
binary evolution, which is believed to be the main evolutionary channel to hot
subdwarf stars. The details of these processes are difficult to model, but
adiabatic expansion provides an excellent approximation to the structure of a
donor star undergoing dynamical time scale mass transfer. We can use this model
to study the responses of stars of various masses and evolutionary stages as
potential donor stars, with the urgent goal of obtaining more accurate
stability criteria for dynamical mass transfer in binary population synthesis
studies. As examples, we describe here several models with the initial masses
equal to 1 Msun and 10 Msun, and identify potential limitations to the use of
our results for giant-branch stars.Comment: 7 pages, 5 figures,Accepted for publication in AP&SS, Special issue
Hot Sub-dwarf Stars, in Han Z., Jeffery S., Podsiadlowski Ph. ed
Spi-OPS : Spitzer and CHEOPS confirm the near-polar orbit of MASCARA-1 b and reveal a hint of dayside reflection
A.C.C. and T.G.W. acknowledge support from STFC consolidated grant number ST/M001296/1.Context. The light curves of tidally locked hot Jupiters transiting fast-rotating, early-type stars are a rich source of information about both the planet and star, with full-phase coverage enabling a detailed atmospheric characterisation of the planet. Although it is possible to determine the true spinâorbit angle Κ â a notoriously difficult parameter to measure â from any transit asymmetry resulting from gravity darkening induced by the stellar rotation, the correlations that exist between the transit parameters have led to large disagreements in published values of Κ for some systems. Aims. We aimed to study these phenomena in the light curves of the ultra-hot Jupiter MASCARA-1 b, which is characteristically similar to well-studied contemporaries such as KELT-9 b and WASP-33 b. Methods. We obtained optical CHaracterising ExOPlanet Satellite (CHEOPS) transit and occultation light curves of MASCARA-1 b, and analysed them jointly with a Spitzer/IRAC 4.5 ÎŒm full-phase curve to model the asymmetric transits, occultations, and phase-dependent flux modulation. For the latter, we employed a novel physics-driven approach to jointly fit the phase modulation by generating a single 2D temperature map and integrating it over the two bandpasses as a function of phase to account for the differing planetâstar flux contrasts. The reflected light component was modelled using the general ab initio solution for a semi-infinite atmosphere. Results. When fitting the CHEOPS and Spitzer transits together, the degeneracies are greatly diminished and return results consistent with previously published Doppler tomography. Placing priors informed by the tomography achieves even better precision, allowing a determination of Κ = 72.1â2.4+2.5 deg. From the occultations and phase variations, we derived dayside and nightside temperatures of 3062â68+66 K and 1720 ± 330 K, respectively.Our retrieval suggests that the dayside emission spectrum closely follows that of a blackbody. As the CHEOPS occultation is too deep to be attributed to blackbody flux alone, we could separately derive geometric albedo Ag = 0.171â0.068+0.066 and spherical albedo As = 0.266â0.100+0.097 from the CHEOPS data, and Bond albedoAB = 0.057â0.101+0.083 from the Spitzer phase curve.Although small, the Ag and As indicate that MASCARA-1 b is more reflective than most other ultra-hot Jupiters, where Hâ absorption is expected to dominate. Conclusions. Where possible, priors informed by Doppler tomography should be used when fitting transits of fast-rotating stars, though multi-colour photometry may also unlock an accurate measurement of Κ. Our approach to modelling the phase variations at different wavelengths provides a template for how to separate thermal emission from reflected light in spectrally resolved James Webb Space Telescope phase curve data.Publisher PDFPeer reviewe
A CHEOPS-enhanced view of the HD 3167 system
A. C. C. and T. G. W. acknowledge support from STFC consolidated grant numbers ST/R000824/1 and ST/V000861/1, and UKSA grant number ST/R003203/1.Much remains to be understood about the nature of exoplanets smaller than Neptune, most of which have been discovered in compact multi-planet systems. With its inner ultra-short period planet b aligned with the star and two larger outer planets d-c on polar orbits, the multi-planet system HD 3167 features a peculiar architecture and offers the possibility to investigate both dynamical and atmospheric evolution processes. To this purpose we combined multiple datasets of transit photometry and radial velocimetry (RV) to revise the properties of the system and inform models of its planets. This effort was spearheaded by CHEOPS observations of HD 3167b, which appear inconsistent with a purely rocky composition despite its extreme irradiation. Overall the precision on the planetary orbital periods are improved by an order of magnitude, and the uncertainties on the densities of the transiting planets b and c are decreased by a factor of 3. Internal structure and atmospheric simulations draw a contrasting picture between HD 3167d, likely a rocky super-Earth that lost its atmosphere through photo-evaporation, and HD 3167c, a mini-Neptune that kept a substantial primordial gaseous envelope. We detect a fourth, more massive planet on a larger orbit, likely coplanar with HD 3167d-c. Dynamical simulations indeed show that the outer planetary system d-c-e was tilted, as a whole, early in the system history, when HD 3167b was still dominated by the star influence and maintained its aligned orbit. RV data and direct imaging rule out that the companion that could be responsible for the present-day architecture is still bound to the HD 3167 system. Similar global studies of multi-planet systems will tell how many share the peculiar properties of the HD 3167 system, which remains a target of choice for follow-up observations and simulations. © 2022 EDP Sciences. All rights reserved.Publisher PDFPeer reviewe
TOI-1338: TESS' First Transiting Circumbinary Planet
We report the detection of the first circumbinary planet (CBP) found by Transiting Exoplanet Survey Satellite (TESS). The target, a known eclipsing binary, was observed in sectors 1 through 12 at 30 minute cadence and in sectors 4 through 12 at 2 minute cadence. It consists of two stars with masses of 1.1 M o˙ and 0.3 M o˙ on a slightly eccentric (0.16), 14.6 day orbit, producing prominent primary eclipses and shallow secondary eclipses. The planet has a radius of âŒ6.9 R â and was observed to make three transits across the primary star of roughly equal depths (âŒ0.2%) but different durations-a common signature of transiting CBPs. Its orbit is nearly circular (e â 0.09) with an orbital period of 95.2 days. The orbital planes of the binary and the planet are aligned to within âŒ1°. To obtain a complete solution for the system, we combined the TESS photometry with existing ground-based radial-velocity observations in a numerical photometric-dynamical model. The system demonstrates the discovery potential of TESS for CBPs and provides further understanding of the formation and evolution of planets orbiting close binary stars
Transit detection of the long-period volatile-rich super-Earth Μ^2 Lupi d with CHEOPS
Stars and planetary system
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