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 2.47h. We find that the NaI 8200A feature is composed of narrow emission lines due 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 red shift measurement from spectra of the H-alpha line, we are able to derive masses for the white dwarf and M dwarf directly (0.41 +/- 0.01 solar masses and 0.096 +/- 0.004 solar masses, respectively). We use a simple model of the CaII 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 solar radii. 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 timescale 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 H-alpha emission from the M dwarf remains to be explained, but the strengh of the line may be due to X-ray heating of the M dwarf due to accretion onto the white dwarf from the M dwarf wind.Comment: 8 pages, 8 figure

Resolved Spectroscopy of M Dwarf/L Dwarf Binaries. II. 2MASS J 17072343-0558249AB

We present IRTF SpeX observations of the M/L binary system 2MASS J17072343-0558249. SpeX imaging resolves the system into a 1"01+/-0.17 visual binary in which both components have red near infrared colors. Resolved low-resolution (R~150) 0.8-2.5 micron spectroscopy reveals strong H2O, CO and FeH bands and alkali lines in the spectra of both components, characteristic of late-type M and L dwarfs. A comparison to a sample of late-type field dwarf spectra indicates spectral types M9 and L3. Despite the small proper motion of the system (0"100+/-0"009 yr^{-1}), imaging observations over 2.5 yr provide strong evidence that the two components share common proper motion. Physical association is also likely due to the small spatial volume occupied by the two components (based on spectrophotometric distances estimates of 15+/-1 pc) as compared to the relatively low spatial density of low mass field stars. The projected separation of the system is 15+/-3 AU, similar to other late-type M and L binaries. Assuming a system age of 0.5-5 Gyr, we estimate the masses of the binary components to be 0.072-0.083 and 0.064-0.077 M_sun, with an orbital period of roughly 150-300 yr. While this is nominally too long a baseline for astrometric mass measurements, the proximity and relatively wide angular separation of the 2MASS J1707-0558AB pair makes it an ideal system for studying the M dwarf/L dwarf transition at a fixed age and metallicity

The first WASP public data release

The WASP (wide angle search for planets) project is an exoplanet transit survey that has been automatically taking wide field images since 2004. Two instruments, one in La Palma and the other in South Africa, continually monitor the night sky, building up light curves of millions of unique objects. These light curves are used to search for the characteristics of exoplanetary transits. This first public data release (DR1) of the WASP archive makes available all the light curve data and images from 2004 up to 2008 in both the Northern and Southern hemispheres. A web interface () to the data allows easy access over the Internet. The data set contains 3 631 972 raw images and 17 970 937 light curves. In total the light curves have 119 930 299 362 data points available between them

Substellar companions and the formation of hot subdwarf stars

"Copyright 2011 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics."We give a brief review over the observational evidence for close substellar companions to hot subdwarf stars. The formation of these core helium-burning objects requires huge mass loss of their red giant progenitors. It has been suggested that besides stellar companions substellar objects in close orbits may be able to trigger this mass loss. Such objects can be easily detected around hot subdwarf stars by medium or high resolution spectroscopy with an RV accuracy at the km s(-1)-level. Eclipsing systems of Vir type stick out of transit surveys because of their characteristic light curves. The best evidence that substellar objects in close orbits around sdBs exist and that they are able to trigger the required mass loss is provided by the eclipsing system SDSS J0820+0008, which was found in the course of the MUCHFUSS project. Furthermore, several candidate systems have been discovered.Final Accepted Versio

Ages for exoplanet host stars

Age is an important characteristic of a planetary system, but also one that is difficult to determine. Assuming that the host star and the planets are formed at the same time, the challenge is to determine the stellar age. Asteroseismology provides precise age determination, but in many cases the required detailed pulsation observations are not available. Here we concentrate on other techniques, which may have broader applicability but also serious limitations. Further development of this area requires improvements in our understanding of the evolution of stars and their age-dependent characteristics, combined with observations that allow reliable calibration of the various techniques.Comment: To appear in "Handbook of Exoplanets", eds. Deeg, H.J. & Belmonte, J.A, Springer (2018

DE Canum Venaticorum : a bright, eclipsing red dwarf–white dwarf binary

Context. Close white dwarf–red dwarf binaries must have gone through a common-envelope phase during their evolution. DE CVn is a detached white dwarf–red dwarf binary with a relatively short (∼8.7 h) orbital period. Its brightness and the presence of eclipses makes this system ideal for a more detailed study. Aims. From a study of photometric and spectroscopic observations of DE CVn we derive the system parameters that we discuss in the framework of common-envelope evolution. Methods. Photometric observations of the eclipses are used to determine an accurate ephemeris. From a model fit to an average lowresolution spectrum of DE CVn, we constrain the temperature of the white dwarf and the spectral type of the red dwarf. The eclipse light curve is analysed and combined with the radial velocity curve of the red dwarf determined from time-resolved spectroscopy to derive constraints on the inclination and the masses of the components in the system. Results. The derived ephemeris is HJDmin = 2 452 784.5533(1) + 0.3641394(2) × E. The red dwarf in DE CVn has a spectral type of M3V and the white dwarf has an effective temperature of 8 000 K. The inclination of the system is 86+3◦ −2 and the mass and radius of the red dwarf are 0.41 ± 0.06 M and 0.37+0.06 −0.007 R, respectively, and the mass and radius of the white dwarf are 0.51+0.06 −0.02 M and 0.0136+0.0008 −0.0002 R, respectively. Conclusions. We found that the white dwarf has a hydrogen-rich atmosphere (DA-type). Given that DE CVn has experienced a common-envelope phase, we can reconstruct its evolution and we find that the progenitor of the white dwarf was a relatively lowmass star (M ≤ 1.6 M). The current age of this system is 3.3−7.3 × 109 years, while it will take longer than the Hubble time for DE CVn to evolve into a semi-detached system

The discovery of WASP-151b, WASP-153b, WASP-156b: Insights on giant planet migration and the upper boundary of the Neptunian desert

To investigate the origin of the features discovered in the exoplanet population, the knowledge of exoplanets’ mass and radius with a good precision (≲10%) is essential. To achieve this purpose the discovery of transiting exoplanets around bright stars is of prime interest. In this paper, we report the discovery of three transiting exoplanets by the SuperWASP survey and the SOPHIE spectrograph with mass and radius determined with a precision better than 15%. WASP-151b and WASP-153b are two hot Saturns with masses, radii, densities and equilibrium temperatures of 0.31−0.03+0.04 MJ, 1.13−0.03+0.03 RJ, 0.22−0.02+0.03 ρJ and 1290−10+20 K, and 0.39−0.02+0.02 MJ, 1.55−0.08+0.10 RJ, 0.11−0.02+0.02 ρJ and 1700−40+40 K, respectively. Their host stars are early G type stars (with mag V ~ 13) and their orbital periods are 4.53 and 3.33 days, respectively. WASP-156b is a super-Neptune orbiting a K type star (mag V = 11.6). It has a mass of 0.128−0.009+0.010 MJ, a radius of 0.51−0.02+0.02 RJ, a density of 1.0−0.1+0.1 ρJ, an equilibrium temperature of 970−20+30 K and an orbital period of 3.83 days. The radius of WASP-151b appears to be only slightly inflated, while WASP-153b presents a significant radius anomaly compared to a recently published model. WASP-156b, being one of the few well characterized super-Neptunes, will help to constrain the still debated formation of Neptune size planets and the transition between gas and ice giants. The estimates of the age of these three stars confirms an already observed tendency for some stars to have gyrochronological ages significantly lower than their isochronal ages. We propose that high eccentricity migration could partially explain this behavior for stars hosting a short period planet. Finally, these three planets also lie close to (WASP-151b and WASP-153b) or below (WASP-156b) the upper boundary of the Neptunian desert. Their characteristics support that the ultra-violet irradiation plays an important role in this depletion of planets observed in the exoplanet population

HAT-P-27b: A hot Jupiter transiting a G star on a 3 day orbit

We report the discovery of HAT-P-27b, an exoplanet transiting the moderately bright G8 dwarf star GSC 0333-00351 (V=12.214). The orbital period is 3.039586 +/- 0.000012 d, the reference epoch of transit is 2455186.01879 +/- 0.00054 (BJD), and the transit duration is 0.0705 +/- 0.0019 d. The host star with its effective temperature 5300 +/- 90 K is somewhat cooler than the Sun, and is more metal-rich with a metallicity of +0.29 +/- 0.10. Its mass is 0.94 +/- 0.04 Msun and radius is 0.90 +/- 0.04 Rsun. For the planetary companion we determine a mass of 0.660 +/- 0.033 MJ and radius of 1.038 +0.077 -0.058 RJ. For the 30 known transiting exoplanets between 0.3 MJ and 0.8 MJ, a negative correlation between host star metallicity and planetary radius, and an additional dependence of planetary radius on equilibrium temperature are confirmed at a high level of statistical significance.Comment: Submitted to ApJ on 2011-01-18. 12 pages, 7 figures, 7 table