The Disappearing Act of KH 15D: Photometric Results from 1995 to 2004

We present results from the most recent (2002-2004) observing campaigns of the eclipsing system KH 15D, in addition to re-reduced data obtained at Van Vleck Observatory (VVO) between 1995 and 2000. Phasing nine years of photometric data shows substantial evolution in the width and depth of the eclipses. The most recent data indicate that the eclipses are now approximately 24 days in length, or half the orbital period. These results are interpreted and discussed in the context of the recent models for this system put forward by Winn et al. and Chiang & Murray-Clay. A periodogram of the entire data set yields a highly significant peak at 48.37 +/- 0.01 days, which is in accord with the spectroscopic period of 48.38 +/- 0.01 days determined by Johnson et al. Another significant peak, at 9.6 days, was found in the periodogram of the out-of-eclipse data at two different epochs. We interpret this as the rotation period of the visible star and argue that it may be tidally locked in pseudosynchronism with its orbital motion. If so, application of Hut's theory implies that the eccentricity of the orbit is e = 0.65 +/- 0.01. Analysis of the UVES/VLT spectra obtained by Hamilton et al. shows that the v sin(i) of the visible star in this system is 6.9 +/- 0.3 km/sec. Using this value of v sin(i) and the measured rotation period of the star, we calculate the lower limit on the radius to be R = (1.3 +/- 0.1), R_Sun, which concurs with the value obtained by Hamilton et al. from its luminosity and effective temperature. Here we assume that i = 90 degrees since it is likely that the spin and orbital angular momenta vectors are nearly aligned.Comment: 55 pages, 18 figures, 1 color figure, to appear the September issue of the Astronomical Journa

New constraints on the presence of debris disks around G 196-3 B and VHS J125601.92–125723.9 b

Context. The existence of warm (protoplanetary) disks around very young isolated planetary and brown dwarf mass objects is known based on near- and mid-infrared flux excesses and millimeter observations. These disks may later evolve into debris disks or rings, although none have been observed or confirmed so far. Little is known about circum(sub)stellar and debris disks around substellar objects. Aims. We aim to investigate the presence of debris disks around two of the closest (~20 pc), young substellar companions, namely G196-3 B and VHS J125601.92–125723.9 b (VHS J1256–1257 b), whose masses straddle the borderline between planets and brown dwarfs. Both are companions at wide orbits (≥100 au) of M-type dwarfs and their ages (50–100 Myr and 150–300 Myr, respectively) are thought to be adequate for the detection of second-generation disks. Methods. We obtained deep images of G196-3 B and VHS J1256–1257 b with the NOrthern Extended Millimeter Array (NOEMA) at 1.3 mm. These data were combined with recently published Atacama Large Millimeter Array (ALMA) and Very Large Array (VLA) data of VHS J1256–1257 b at 0.87 mm and 0.9 cm, respectively. Results. Neither G196-3 B nor VHS J1256–1257 b were detected in the NOEMA, ALMA, and VLA data. At 1.3 mm, we imposed flux upper limits of 0.108 mJy (G196-3 B) and 0.153 mJy (VHS J1256–1257 b) with a 3-σ confidence. Using the flux upper limits at the millimeter and radio wavelength regimes, we derived maximum values of 1.38×10−2 MEarth and 5.46 × 10−3 MEarth for the mass of any cold dust that might be surrounding G196-3 B and VHS J1256–1257 b, respectively. Conclusions. We put our results in the context of other deep millimeter observations of free-floating and companion objects with substellar masses smaller than 20 MJup and ages between approximately one and a few hundred million years. Only two very young (2–5.4 Myr) objects are detected out of a few tens of them. This implies that the disks around these very low-mass objects must have small masses, and possibly reduced sizes, in agreement with findings by other groups. If debris disks around substellar objects scale down (in mass and size) in a similar manner as protoplanetary disks do, millimeter observations of moderately young brown dwarfs and planets must be at least two orders of magnitude deeper to be able to detect and characterize their surrounding debris disks

THE K2-ESPRINT PROJECT. V. A SHORT-PERIOD GIANT PLANET ORBITING A SUBGIANT STAR

We report on the discovery and characterization of the transiting planet K2-39b (EPIC 206247743b). With an orbital period of 4.6 days, it is the shortest-period planet orbiting a subgiant star known to date. Such planets are rare, with only a handful of known cases. The reason for this is poorly understood but may reflect differences in planet occurrence around the relatively high-mass stars that have been surveyed, or may be the result of tidal destruction of such planets. K2-39 (EPIC 206247743) is an evolved star with a spectroscopically derived stellar radius and mass of 3.88 [subscript -0.42] [superscript +0.48] R [subscript ⊙] and 1.53[subscript-0.12] [superscript +0.13] M[subscript ⊙], respectively, and a very close-in transiting planet, with a/R [subscript asterisk]= 3.4 Radial velocity (RV) follow-up using the HARPS, FIES, and PFS instruments leads to a planetary mass of 50.3 [subscript -9.4] [superscript +9.7] M [subscript ⊙]. In combination with a radius measurement of 8.3 ± 1.1 R [subscript oplus], this results in a mean planetary density of 0.50 [subscript -0.17] [superscript +0.29] g cm [superscript -3]. We furthermore discover a long-term RV trend, which may be caused by a long-period planet or stellar companion. Because K2-39b has a short orbital period, its existence makes it seem unlikely that tidal destruction is wholly responsible for the differences in planet populations around subgiant and main-sequence stars. Future monitoring of the transits of this system may enable the detection of period decay and constrain the tidal dissipation rates of subgiant stars

First Detection of Two Superoutbursts during Rebrightening Phase of a WZ Sge-type Dwarf Nova: TCP J21040470+4631129

We report photometric and spectroscopic observations and analysis of the 2019 superoutburst of TCP J21040470+4631129. This object showed a 9-mag superoutburst with early superhumps and ordinary superhumps, which are the features of WZ Sge-type dwarf novae. Five rebrightenings were observed after the main superoutburst. The spectra during the post-superoutburst stage showed the Balmer, He I and possible sodium doublet features. The mass ratio is derived as 0.0880(9) from the period of the superhump. During the third and fifth rebrightenings, growing superhumps and superoutbursts were observed, which have never been detected during a rebrightening phase among WZ Sge-type dwarf novae with multiple rebrightenings. To induce a superoutburst during the brightening phase, the accretion disk was needed to expand beyond the 3:1 resonance radius of the system again after the main superoutburst. These peculiar phenomena can be explained by the enhanced viscosity and large radius of the disk suggested by the higher luminosity and the presence of late-stage superhumps during the post-superoutburst stage, plus by more mass supply from the cool mass reservoir and/or from the secondary because of the enhanced mass transfer than those of other WZ Sge-type dwarf novae.Comment: 13 pages, 10 figures, accepted for publication in PAS

GTC/CanariCam Deep Mid-infrared Imaging Survey of Northern Stars within 5 pc

© 2021. The Author(s). Published by the American Astronomical Society. This is an open access article distributed under the Creative Commons Attribution License, to view a copy of the license, see: https://creativecommons.org/licenses/by/4.0/In this work we present the results of a direct imaging survey for brown dwarf companions around the nearest stars at the mid-infrared 10 micron range (λ c = 8.7 μm, Δλ = 1.1 μm) using the CanariCam instrument on the 10.4 m Gran Telescopio Canarias (GTC). We imaged the 25 nearest stellar systems within 5 pc of the Sun at declinations δ > −25° (at least half have planets from radial-velocity studies), reaching a mean detection limit of 11.3 ± 0.2 mag (1.5 mJy) in the Si-2 8.7 μm band over a range of angular separations from 1″ to 10″. This would have allowed us to uncover substellar companions at projected orbital separations between ∼2 and 50 au, with effective temperatures down to 600 K and masses greater than 30 M Jup assuming an average age of 5 Gyr and masses down to the deuterium-burning mass limit for objects with ages <1 Gyr. From the nondetection of such companions, we determined upper limits on their occurrence rate at depths and orbital separations yet unexplored by deep imaging programs. For the M dwarfs, the main component of our sample, we found with a 90% confidence level that fewer than 20% of these low-mass stars have L- and T-type brown dwarf companions with m ≳ 30 MJup and Teff ≳ 600 K at ∼3.5–35 au projected orbital separations.Peer reviewedFinal Published versio