We report the discovery of WTS-2 b, an unusually close-in 1.02-d hot Jupiter (M_P_=1.12M_J_, R_P_=1.30R_J_) orbiting a K2V star, which has a possible gravitationally bound M-dwarf companion at 0.6-arcsec separation contributing ~20% of the total flux in the observed J-band light curve. The planet is only 1.5 times the separation from its host star at which it would be destroyed by Roche lobe overflow, and has a predicted remaining lifetime of just ~40Myr, assuming a tidal dissipation quality factor of Q'_*_=10^6^. Q'_*_ is a key factor in determining how frictional processes within a host star affect the orbital evolution of its companion giant planets, but it is currently poorly constrained by observations. We calculate that the orbital decay of WTS-2 b would correspond to a shift in its transit arrival time of T_shift_~17s after 15yr assuming Q'_*_=10^6^. A shift less than this would place a direct observational constraint on the lower limit of Q'_*_ in this system. We also report a correction to the previously published expected T_shift_ for WASP-18 b, finding that T_shift_=356s after 10yr for Q'_*_10^6^, which is much larger than the estimated 28s quoted in WASP-18 b discovery paper. We attempted to constrain Q'_*_ via a study of the entire population of known transiting hot Jupiters, but our results were inconclusive, requiring a more detailed treatment of transit survey sensitivities at long periods. We conclude that the most informative and straightforward constraints on Q'_*_ will be obtained by direct observational measurements of the shift in transit arrival times in individual hot Jupiter systems. We show that this is achievable across the mass spectrum of exoplanet host stars within a decade, and will directly probe the effects of stellar interior structure on tidal dissipation.
Star formation theory predicts that short-period M-dwarf binaries with highly unequal-mass components are rare. First, the mass ratio of close binary systems is driven to unity due to the secondary preferentially accreting gas with high angular momentum. Secondly, both dynamical decay of multiple systems and interactions with tertiary stars that tighten the binary orbit will eject the lowest mass member. Generally, only the two most massive stars are paired after such interactions, and the frequency of tight unequal-mass binaries is expected to decrease steeply with primary mass. In this paper, we present the discovery of a highly unequal-mass eclipsing M-dwarf binary, providing a unique constraint on binary star formation theory and on evolutionary models for low-mass binary stars. The binary is discovered using high-precision infrared light curves from the United Kingdom Infrared Telescope (UKIRT) Wide Field Camera (WFCAM) Transit Survey and has an orbital period of 2.44d. We find stellar masses of M_1_=0.53(+/-0.02)M_{sun}_ and M_2_=0.143(+/-0.006)M_{sun}_ (mass ratio 0.27), and radii of R_1_=0.51(+/-0.01)R_{sun}_ and R_2_=0.174(+/-0.006)R_{sun}_. This puts the companion in a very sparsely sampled and important late M-dwarf mass regime. Since both stars will share the same age and metallicity and straddle the theoretical boundary between fully and partially convective stellar interiors, a comparison can be made to model predictions over a large range of M-dwarf masses using the same model isochrone. Both stars appear to have a slightly inflated radius compared to 1Gyr` model predictions for their masses, but future work is needed to properly account for the effects of star spots on the light-curve solution. A significant, subsynchronous, ~2.56d signal with ~2% peak-to-peak amplitude is detected in the WFCAM light curve, which we attribute to rotational modulation of cool star spots. We propose that the subsynchronous rotation is either due to a stable star-spot complex at high latitude on the (magnetically active) primary (i.e. differential rotation), or additional magnetic braking, or interaction of the binary with a third body or circumbinary disc during its pre-main-sequence phase.
We report CCD optical (B and V passbands) and near IR (J and K bands) observations in the region of the old open cluster NGC 2141. By combining the two sets of photometry (500 stars in common) we derive new estimates of the cluster's fundamental parameters. We confirm that the cluster is 2.5Gyrs old, but, with respect to previous investigations, we obtain a slightly larger reddening (E(B-V)=0.40), and a slightly shorter distance (3.8kpc) from the Sun. Finally, we present the Luminosity Function (LF) in the V band, which is another age indicator. We provide a good fit for the age range inferred from isochrones by assuming the Kroupa et al. (1993MNRAS.262..545K) IMF up to M_V_=5.0. We interpret the disagreement at fainter magnitudes as evidence of mass segregation.
We present a photometric survey of bright southern stars carried out using the DENIS instrument equipped with attenuating filters. The observations were carried out not using the survey mode of DENIS, but with individual target pointings. This project was stimulated by the need to obtain near-infrared photometry of stars to be used in early commissioning observations of the ESO Very Large Telescope Interferometer, and in particular to establish a network of bright calibrator sources. We stress that near-infrared photometry is peculiarly lacking for many bright stars. These stars are saturated in 2MASS as well as in regular DENIS observations. The only other observations available for bright infrared stars are those of the Two Micron Sky Survey (<II/2>) dating from over thirty years ago. These were restricted to declinations above -30{deg} and thus cover only about half of the sky accessible from the VLTI site. We note that the final 2MASS data release includes photometry of bright stars, obtained by means of point-spread function fitting. However, this method only achieves about 30 percent accuracy, which is not sufficient for most applications. In this work, we present photometry for over 600 stars, each with at least one and up to eight measurements, in the J and K filters. Typical accuracy is at the level of 0.05mag and 0.04mag in the J and Ks bands, respectively.
A review of star formation in the Rho Ophiuchi molecular complex is presented, with particular emphasis on studies of the main cloud, L1688, since 1991. Recent photometric and parallax measurements of stars in the Upper Scorpius subgroup of the Sco-Cen OB association suggest a distance for the cloud between 120 and 140 parsecs. Star formation is ongoing in the dense cores of L1688 with a median age for young stellar objects of 0.3Myr. The surface population appears to have a median age of 2-5Myr and merges with low mass stars in the Upper Scorpius subgroup. Making use of the most recent X-ray and infrared photometric surveys and spectroscopic surveys of L1688, we compile a list of over 300 association members with counterparts in the 2MASS catalog. Membership criteria, such as lithium absorption, X-ray emission, and infrared excess, cover the full range of evolutionary states for young stellar objects. Spectral energy distributions are classified for many association members using infrared photometry obtained from the Spitzer Space Telescope.
In some scenarios for the formation of the Milky Way bulge, the stellar population at the edges of the boxy bulge may be younger than those on the minor axis or close to the Galactic center. So far the only bulge region where deep color-magnitude diagrams have been obtained is indeed along the minor axis. To overcome this limitation, we aim to age-date the bulge stellar populations far away from the bulge minor axis. Color-magnitude diagrams and luminosity functions have been obtained from deep near-IR VLT/HAWK-I images taken at the two Southern corners of the boxy bulge, i.e., near the opposite edges of the Galactic bar. The foreground disk contamination has been statistically removed using a pure disk field observed with the same instrument and located approximately at similar Galactic latitudes of the two bulge fields and ~30{deg} in longitude away from the Galactic center. For each bulge field, mean reddening and distance are determined using the position of red clump stars, and the metallicity distribution is derived photometrically using the color distribution of stars in the upper red giant branch.
We have used the Keck 10m telescope to count objects as a function of image size in two high Galactic latitude fields covering 1.5arcmin^2^ and reaching 50% completeness depths of K=24 and J=24.5 for stellar sources. Our counts extend ~1mag deeper in K than those of surveys with other telescopes; complement other Keck surveys in the K-band that provide counts at comparable or shallower depths but that have not utilized image structure; and extend by several magnitudes the J-band counts from brighter surveys using smaller telescopes that cover larger areas.
We present wide field near-infrared (near-IR) photometry of 12 Galactic globular clusters, typically extending from the tip of the cluster red giant branch (RGB) to the main sequence turnoff. Using recent homogenous values of cluster distance, reddening and metallicity, the resulting photometry is directly compared to the predictions of several recent libraries of stellar evolutionary models. Of the sets of models investigated, Dartmouth and Victoria-Regina models best reproduce the observed RGB morphology, albeit with offsets in J-K_S_ color which vary in their significance in light of all sources of observational uncertainty. Therefore, we also present newly recalibrated relations between near-IR photometric indices describing the upper RGB versus cluster iron abundance as well as global metallicity. The influence of enhancements in alpha elements and helium are analyzed, and we find that the former affect the morphology of the upper RGB in accord with model predictions. Meanwhile, the empirical relations we derive are in good agreement with previous results, and minor discrepancies can likely be attributed to differences in the assumed cluster distances and reddenings. In addition, we present measurements of the horizontal branch (HB) and RGB bump magnitudes, finding a non-negligible dependence of the near-IR HB magnitude on cluster metallicity. Lastly, we discuss the influence of assumed cluster distances, reddenings and metallicities on our results, finding that our empirical relations are generally insensitive to these factors to within their uncertainties.
Infrared JKs-band photometry of the Galactic globular clusters M15 and, for the first time, M56 is presented. We estimate the reddening [E(B-V) = 0.18 {=/-} 0.08 mag] and distance modulus [(m - M)V = 15.43 {+/-} 0.30 mag] toward the poorly studied globular cluster M56. We combine our data with observations of other clusters from the literature (12 in total) to extend the [Fe/H] versus red giant branch (RGB) slope relation toward metal-poor clusters.
Globular clusters are the oldest stellar systems in the Milky Way, and they probe the early epoch of the Galaxy formation. However, the uncertainties on their absolute age are still too large to soundly constrain how the Galactic structures have assembled. The aim of this work is to obtain an accurate estimate of the absolute age of the globular cluster NGC 2808 using deep IR data obtained with the multi-conjugate adaptive optics system operating at the Gemini South telescope (GeMS). This exquisite photometry, combined with that obtained in V and I-bands with HST, allowed us to detect the faint Main Sequence Knee feature in NGC 2808 colour magnitude diagram. The difference between this point and the main sequence turn-off is a good age estimator that provides ages with unprecedented accuracy.
