Discovery of a Low-Mass Companion to the Solar-Type Star Tyc 2534-698-1 (original) (raw)
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2012
We report the discovery via radial velocity measurements of a short-period (P = 2.430420 ± 0.000006 days) companion to the F-type main sequence star TYC 2930-00872-1. A long-term trend in the radial velocity data also suggests the presence of a tertiary stellar companion with P > 2000 days. High-resolution spectroscopy of the host star yields T eff = 6427 ± 33 K, log g = 4.52 ± 0.14, and [Fe/H]=−0.04 ± 0.05. These parameters, combined with the broad-band spectral energy distribution and a parallax, allow us to infer a mass and radius of the host star of M 1 = 1.21 ± 0.08 M ⊙ and R 1 = 1.09 +0.15 −0.13 R ⊙. The minimum mass of the inner companion is below the hydrogen burning limit, however the true mass is likely to be substantially higher. We are able to exclude transits of the inner companion with high confidence. Further, the host star spectrum exhibits a clear signature of Ca H and K core emission indicating stellar activity, but a lack of photometric variability and small v sin I suggest the primary's spin axis is oriented in a pole-on configuration. The rotational period of the primary estimated through an activity-rotation relation matches the orbital period of the inner companion to within 1.5 σ, suggesting that the primary and inner companion are tidally locked. If the inner companion's orbital angular momentum vector is aligned with the stellar spin axis as expected through tidal evolution, then it has a stellar mass of ∼ 0.3 − 0.4 M ⊙. Direct imaging limits the existence of stellar companions to projected separations < 30 AU. No set of spectral lines and no significant flux contribution to the spectral energy distribution from either companion are detected, which places individual upper mass limits of M {2,3} 1.0 M ⊙ , provided they are not stellar remnants. If the tertiary is not a stellar remnant, then it likely has a mass of ∼ 0.5 − 0.6 M ⊙ , and its orbit is likely significantly inclined from that of the secondary, suggesting that the Kozai-Lidov mechanism may have driven the dynamical evolution of this system.
A brown dwarf companion to the intermediate-mass star HR 6037
Astronomy and Astrophysics, 2010
Context. The frequency of brown dwarf and planetary-mass companions to intermediate-mass stars is still unknown. Imaging and radial velocity surveys have revealed a small number of substellar companions to these stars. Aims. In the course of an imaging survey we have detected a visual companion to the intermediate-mass star HR 6037. In this letter we confirm it as a co-moving substellar object. Methods. We present two epoch adaptive optics observations of HR 6037, an A6-type star with a companion candidate at 6. ′′ 67 and position angle of 294 degrees. We also analyze near-infrared spectroscopy of the companion. Results. Two epoch observations of HR 6037 have allowed us to confirm HR 6037 B as a co-moving companion. Its J and H band spectra suggest the object has an spectral type of M9, with a surface gravity intermediate between a 10 Myr dwarf and a field dwarf of the same spectral type. The comparison of its K s-band photometry with evolutionary tracks allows us to derive a mass, effective temperature, and surface gravity of 62±20 M Jup , T eff = 2330 ± 200 K, and log g = 5.1 ± 0.2, respectively. The small mass ratio of the binary, ∼0.03, and its long orbital period, ∼5000 yr, makes HR 6037 a rare and uncommon binary system.
Discovery of a Young Planetary Mass Companion to the Nearby M Dwarf VHS J125601.92-125723.9
The Astrophysical Journal, 2015
In a search for common proper motion companions using the VISTA Hemisphere Survey (VHS) and the 2MASS catalogs we have identified a very red (J − K s = 2.47 mag) late-L dwarf companion of a previously unrecognized M dwarf VHS J125601.92-125723.9 (hereafter VHS 1256-1257), located at a projected angular separation of 8. 06 ± 0. 03. In this work we present a suite of astrometric, photometric, and spectroscopic observations of this new pair in an effort to confirm the companionship and characterize the components. From low-resolution (R ∼ 130-600) optical and near-infrared spectroscopy we classified the primary and the companion as an M7.5 ± 0.5 and L7 ± 1.5, respectively. The primary shows slightly weaker alkali lines than field dwarfs of similar spectral type, but still consistent with either a high-gravity dwarf or a younger object of hundreds of millions of years. The secondary shows spectral features characteristic for low surface gravity objects at ages below several hundred million years, like the peaked triangular shape of the H-band continuum and alkali lines weaker than in field dwarfs of the same spectral type. The absence of lithium in the atmosphere of the primary and the likely kinematic membership to the Local Association allowed us to constrain the age of the system to the range of 150-300 Myr. We report a measurement of the trigonometric parallax π = 78.8 ± 6.4 mas, which translates into a distance of 12.7 ± 1.0 pc; the pair thus has a projected physical separation of 102 ± 9 AU. We derived the bolometric luminosities of the components and compared them with theoretical evolutionary models to estimate the masses and effective temperatures. For the primary, we determined a luminosity of log(L bol /L) = −3.14 ± 0.10, and inferred a mass of 73 +20 −15 M Jup at the boundary between stars and brown dwarfs and an effective temperature of 2620 ± 140 K. For the companion we obtained a luminosity of log(L bol /L) = −5.05 ± 0.22 and a mass of 11.2 +9.7 −1.8 M Jup placing it near the deuterium-burning mass limit. The effective temperature derived from evolutionary models is 880 +140 −110 K, about 400-700 K cooler than the temperature expected for field late-L dwarfs.
Astronomy & Astrophysics
Context. Our knowledge of populations and the occurrence of planets orbiting evolved intermediate-mass stars is still incomplete. In 2010 we started a planet search programme among 95 giant stars observed by the Kepler mission to increase the sample of giant stars with planets and with reliable estimates of stellar masses and radii. Aims. We present the two systems from our planet search programme whose companions we were able to characterise: KIC 3526061 and HD 187878. Methods. We used precise stellar radial velocity measurements taken with four different echelle spectrographs to derive an orbital solution. We used Gaia astrometric measurements to obtain the inclination of the HD 187878 system and Kepler photometric observations to estimate the stellar mass and radius. Results. We report the discovery of a sub-stellar companion and a stellar companion around two intermediate-mass red giant branch stars. KIC 3526061 b is most likely a brown dwarf with a minimum mass of 18.15 ± 0.44 ...
Direct Imaging Discovery of a Young Brown Dwarf Companion to an A2V Star
The Astrophysical Journal, 2020
We present the discovery and spectroscopy of HIP 75056Ab, a companion directly imaged at a very small separation of 0. 125 to an A2V star in the Scorpius-Centaurus OB2 association. Our observations utilized VLT/SPHERE between 2015−2019, enabling low-resolution spectroscopy (0.95−1.65 µm), dual-band imaging (2.1−2.25 µm), and relative astrometry over a four-year baseline. HIP 75056Ab is consistent with spectral types in the range of M6−L2 and T eff ∼ 2000−2600 K. A comparison of the companion's brightness to evolutionary tracks suggests a mass of ∼20−30 M Jup. The astrometric measurements are consistent with an orbital semi-major axis of ∼15−45 au and an inclination close to face-on (i 35 o). In this range of mass and orbital separation, HIP 75056Ab is likely at the lowmass end of the distribution of companions formed via disk instability, although a formation of the companion via core accretion cannot be excluded. The orbital constraints are consistent with the modest eccentricity values predicted by disk instability, a scenario that can be confirmed by further astrometric monitoring. HIP 75056Ab may be utilized as a low-mass atmospheric comparison to older, higher-mass brown dwarfs, and also to young giant planets. Finally, the detection of HIP 75056Ab at 0. 125 represents a milestone in detecting low-mass companions at separations corresponding to the habitable zones of nearby Sun-like stars.
Discovery of Two T Dwarf Companions with theSpitzer Space Telescope
The Astrophysical Journal, 2007
During an ongoing survey of 5 0 ; 5 0 fields surrounding stars in the solar neighborhood with the Infrared Array Camera aboard the Spitzer Space Telescope, we identified these companions as candidate T dwarfs based on their mid-infrared colors. Using near-infrared spectra obtained with SpeX at the NASA Infrared Telescope Facility, we confirm the presence of methane absorption that characterizes T dwarfs and measure spectral types of T2:5 AE 0:5 and T7:5 AE 0:5 for HN Peg B and HD 3651B, respectively. By comparing our Spitzer data to images from the Two Micron All Sky Survey obtained several years earlier, we find that the proper motions of HN Peg B and HD 3651B are consistent with those of the primaries, confirming their companionship. A comparison of their luminosities to the values predicted by theoretical evolutionary models implies masses of 0:021 AE 0:009 and 0:051 AE 0:014 M for HN Peg B and HD 3651B, respectively. In addition, the models imply an effective temperature for HN Peg B that is significantly lower than the values derived for other T dwarfs at similar spectral types, which is the same behavior reported by Metchev & Hillenbrand for the young late L dwarf HD 203030B. Thus, the temperature of the L/T transition appears to depend on surface gravity. Meanwhile, HD 3651B is the first substellar companion directly imaged around a star that is known to harbor a close-in planet from radial velocity surveys. The discovery of this companion supports the notion that the high eccentricities of close-in planets like that near HD 3651 may be the result of perturbations by low-mass companions at wide separations.
The Astronomical Journal, 2013
We describe the discovery of a likely brown dwarf (BD) companion with a minimum mass of 31.7 ± 2.0 M Jup to GSC 03546-01452 from the MARVELS radial velocity survey, which we designate as MARVELS-6b. For reasonable priors, our analysis gives a probability of 72% that MARVELS-6b has a mass below the hydrogen-burning limit of 0.072 M ⊙ , and thus it is a high-confidence BD companion. It has a moderately long orbital period of 47.8929 +0.0063 −0.0062 days with a low eccentricty of 0.1442 +0.0078 −0.0073 , and a semi-amplitude of 1644 +12 −13 m s −1 . Moderate resolution spectroscopy of the host star has determined the following parameters: T eff = 5598 ± 63, log g = 4.44 ± 0.17, and [Fe/H] = +0.40 ± 0.09. Based upon these measurements, GSC 03546-01452 has a probable mass and radius of M * = 1.11 ± 0.11 M ⊙ and R * = 1.06 ± 0.23 R ⊙ with an age consistent with less than ∼6 Gyr at a distance of 219 ± 21 pc from the Sun. Although MARVELS-6b is not observed to transit, we cannot definitively rule out a transiting configuration based on our observations. There is a visual companion detected with Lucky Imaging at 7.7 ′′ from the host star, but our analysis shows that it is not bound to this system. The minimum mass of MARVELS-6b exists at the minimum of the mass functions for both stars and planets, making this a rare object even compared to other BDs. It also exists in an underdense region in both period/eccentricity and metallicity/eccentricity space.
Discovery of a brown dwarf companion to the star HIP 64892
Astronomy & Astrophysics, 2018
We report the discovery of a bright, brown dwarf companion to the star HIP 64892, imaged with VLT/SPHERE during the SHINE exoplanet survey. The host is a B9.5V member of the Lower-Centaurus-Crux subgroup of the Scorpius Centaurus OB association. The measured angular separation of the companion (1.2705 ± 0.0023”) corresponds to a projected distance of 159 ± 12 AU. We observed the target with the dual-band imaging and long-slit spectroscopy modes of the IRDIS imager to obtain its spectral energy distribution (SED) and astrometry. In addition, we reprocessed archival NACO L-band data, from which we also recover the companion. Its SED is consistent with a young (<30 Myr), low surface gravity object with a spectral type of M9γ ± 1. From comparison with the BT-Settl atmospheric models we estimate an effective temperature of Teff = 2600 ± 100 K, and comparison of the companion photometry to the COND evolutionary models yields a mass of ~29−37 MJ at the estimated age of 16−7+15 Myr for t...
Astronomy & Astrophysics, 2021
We report the discovery of five transiting companions near the hydrogen-burning mass limit in close orbits around main sequence stars originally identified by the Transiting Exoplanet Survey Satellite (TESS) as TESS objects of interest (TOIs): TOI-148, TOI-587, TOI-681, TOI-746, and TOI-1213. Using TESS and ground-based photometry as well as radial velocities from the CORALIE, CHIRON, TRES, and FEROS spectrographs, we found the companions have orbital periods between 4.8 and 27.2 days, masses between 77 and 98 MJup , and radii between 0.81 and 1.66 RJup . These targets have masses near the uncertain lower limit of hydrogen core fusion (~73-96 MJup ), which separates brown dwarfs and low-mass stars. We constrained young ages for TOI-587 (0.2 ± 0.1 Gyr) and TOI-681 (0.17 ± 0.03 Gyr) and found them to have relatively larger radii compared to other transiting companions of a similar mass. Conversely we estimated older ages for TOI-148 and TOI-746 and found them to have relatively smalle...