Orbital and spectral analysis of the benchmark brown dwarf HD 4747B

Context. The study of high-contrast imaged brown dwarfs and exoplanets depends strongly on evolutionary models. To estimate the mass of a directly imaged substellar object, its extracted photometry or spectrum is used and adjusted with model spectra together with the estimated age of the system. These models still need to be properly tested and constrained. HD 4747B is a brown dwarf close to the H burning mass limit, orbiting a nearby (d = 19.25 ± 0.58 pc), solar-type star (G9V); it has been observed with the radial velocity method for over almost two decades. Its companion was also recently detected by direct imaging, allowing a complete study of this particular object. Aims. We aim to fully characterize HD 4747B by combining a well-constrained dynamical mass and a study of its observed spectral features in order to test evolutionary models for substellar objects and to characterize its atmosphere. Methods. We combined the radial velocity measurements of High Resolution Echelle Spectrometer (HIRES) and CORALIE taken over two decades and high-contrast imaging of several epochs from NACO, NIRC2, and SPHERE to obtain a dynamical mass. From the SPHERE data we obtained a low-resolution spectrum of the companion from Y to H band, and two narrow band-width photometric measurements in the K band. A study of the primary star also allowed us to constrain the age of the system and its distance. Results. Thanks to the new SPHERE epoch and NACO archival data combined with previous imaging data and high-precision radial velocity measurements, we were able to derive a well-constrained orbit. The high eccentricity (e = 0.7362 ± 0.0025) of HD 4747B is confirmed, and the inclination and the semi-major axis are derived (i = 47.3 ± 1.6°, a = 10.01 ± 0.21 au). We derive a dynamical mass of mB = 70.0 ± 1.6 MJup, which is higher than a previous study but in better agreement with the models. By comparing the object with known brown dwarfs spectra, we derive a spectral type of L9 and an effective temperature of 1350 ± 50 K. With a retrieval analysis we constrain the oxygen and carbon abundances and compare them with the values from the HR 8799 planets.

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Spectral and atmospheric characterisation of a new benchmark brown dwarf HD 13724 B

Astronomy and Astrophysics ◽

10.1051/0004-6361/202037524 ◽

2020 ◽

Vol 635 ◽

pp. A203 ◽

Cited By ~ 3

Author(s):

E. L. Rickman ◽

D. Ségransan ◽

J. Hagelberg ◽

J.-L. Beuzit ◽

A. Cheetham ◽

...

Keyword(s):

Radial Velocity ◽

High Contrast ◽

Imaging Data ◽

Brown Dwarf ◽

Low Resolution ◽

Contrast Imaging ◽

Echelle Spectrograph ◽

Dynamical Mass ◽

High Contrast Imaging ◽

Mass Estimate

Context. HD 13724 is a nearby solar-type star at 43.48 ± 0.06 pc hosting a long-period low-mass brown dwarf detected with the CORALIE echelle spectrograph as part of the historical CORALIE radial-velocity search for extra-solar planets. The companion has a minimum mass of 26.77−2.2+4.4 MJup and an expected semi-major axis of ~240 mas making it a suitable target for further characterisation with high-contrast imaging, in particular to measure its inclination, mass, and spectrum and thus establish its substellar nature. Aims. Using high-contrast imaging with the SPHERE instrument on the Very Large Telescope (VLT), we are able to directly image a brown dwarf companion to HD 13724 and obtain a low-resolution spectrum. Methods. We combine the radial-velocity measurements of CORALIE and HARPS taken over two decades and high-contrast imaging from SPHERE to obtain a dynamical mass estimate. From the SPHERE data we obtain a low-resolution spectrum of the companion from Y to J band, as well as photometric measurements from IRDIS in the J, H, and K bands. Results. Using high-contrast imaging with the SPHERE instrument at the VLT, we report the first images of a brown dwarf companion orbiting the host star HD 13724. It has an angular separation of 175.6 ± 4.5 mas and an H-band contrast of 10.61 ± 0.16 mag, and using the age estimate of the star to be ~1 Gyr gives an isochronal mass estimate of ~44 MJup. By combining radial-velocity and imaging data we also obtain a dynamical mass of 50.5−3.5+3.3 MJup. Through fitting an atmospheric model, we estimate a surface gravity of logg = 5.5 and an effective temperature of 1000 K. A comparison of its spectrum with observed T dwarfs estimates a spectral type of T4 or T4.5, with a T4 object providing the best fit.

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Orbital and spectral characterization of the benchmark T-type brown dwarf HD 19467B

Astronomy and Astrophysics ◽

10.1051/0004-6361/202037984 ◽

2020 ◽

Vol 639 ◽

pp. A47

Author(s):

A.-L. Maire ◽

K. Molaverdikhani ◽

S. Desidera ◽

T. Trifonov ◽

P. Mollière ◽

...

Keyword(s):

High Surface ◽

Formation Mechanisms ◽

Evolutionary Models ◽

Imaging Data ◽

Brown Dwarf ◽

Contrast Imaging ◽

Nearby Star ◽

Dynamical Mass ◽

Orbital Parameters ◽

Bolometric Luminosity

Context. Detecting and characterizing substellar companions for which the luminosity, mass, and age can be determined independently is of utter importance to test and calibrate the evolutionary models due to uncertainties in their formation mechanisms. HD 19467 is a bright and nearby star hosting a cool brown dwarf companion detected with radial velocities and imaging, making it a valuable object for such studies. Aims. We aim to further characterize the orbital, spectral, and physical properties of the HD 19467 system. Methods. We present new high-contrast imaging data with the SPHERE and NaCo instruments. We also analyze archival data from the instruments HARPS, NaCo, HIRES, UVES, and ASAS. Furthermore, we use proper motion data of the star from HIPPARCOS and Gaia. Results. We refined the properties of the host star and derived an age of 8.0+2.0−1.0 Gyr based on isochrones, gyrochronology, and chemical and kinematic arguments. This age estimate is slightly younger than previous age estimates of ~9–11 Gyr based on isochrones. No orbital curvature is seen in the current imaging, radial velocity, and astrometric data. From a joint fit of the data, we refined the orbital parameters for HD 19467B, including: a period of 398+95−93 yr, an inclination of 129.8+8.1−5.1 deg, an eccentricity of 0.56 ± 0.09, a longitude of the ascending node of 134.8 ± 4.5 deg, and an argument of the periastron of 64.2+5.5−6.3 deg. We assess a dynamical mass of 74+12−9 MJ. The fit with atmospheric models of the spectrophotometric data of the companion indicates an atmosphere without clouds or with very thin clouds, an effective temperature of 1042+77−71 K, and a high surface gravity of 5.34+0.8−0.9 dex. The comparison to model predictions of the bolometric luminosity and dynamical mass of HD 19467B, assuming our system age estimate, indicates a better agreement with the Burrows et al. (1997, ApJ, 491, 856) models; whereas, the other evolutionary models used tend to underestimate its cooling rate.

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Constraining the properties of HD 206893 B

Astronomy and Astrophysics ◽

10.1051/0004-6361/201935044 ◽

2019 ◽

Vol 627 ◽

pp. L9 ◽

Cited By ~ 8

Author(s):

A. Grandjean ◽

A.-M. Lagrange ◽

H. Beust ◽

L. Rodet ◽

J. Milli ◽

...

Keyword(s):

Radial Velocity ◽

Semimajor Axis ◽

High Contrast ◽

Brown Dwarf ◽

Contrast Imaging ◽

Dynamical Mass ◽

Orbital Parameters ◽

High Contrast Imaging ◽

Very Large Telescope ◽

Astrometric Data

Context. High contrast imaging enables the determination of orbital parameters for substellar companions (planets, brown dwarfs) from the observed relative astrometry and the estimation of model and age-dependent masses from their observed magnitudes or spectra. Combining astrometric positions with radial velocity gives direct constraints on the orbit and on the dynamical masses of companions. A brown dwarf was discovered with the VLT/SPHERE instrument at the Very Large Telescope (VLT) in 2017, which orbits at ∼11 au around HD 206893. Its mass was estimated between 12 and 50 MJ from evolutionary models and its photometry. However, given the significant uncertainty on the age of the system and the peculiar spectrophotometric properties of the companion, this mass is not well constrained. Aims. We aim at constraining the orbit and dynamical mass of HD 206893 B. Methods. We combined radial velocity data obtained with HARPS spectra and astrometric data obtained with the high contrast imaging VLT/SPHERE and VLT/NaCo instruments, with a time baseline less than three years. We then combined those data with astrometry data obtained by HIPPARCOS and Gaia with a time baseline of 24 yr. We used a Markov chain Monte Carlo approach to estimate the orbital parameters and dynamical mass of the brown dwarf from those data. Results. We infer a period between 21 and 33 yr and an inclination in the range 20−41° from pole-on from HD 206893 B relative astrometry. The RV data show a significant RV drift over 1.6 yr. We show that HD 206893 B cannot be the source of this observed RV drift as it would lead to a dynamical mass inconsistent with its photometry and spectra and with HIPPARCOS and Gaia data. An additional inner (semimajor axis in the range 1.4–2.6 au) and massive (∼15 MJ) companion is needed to explain the RV drift, which is compatible with the available astrometric data of the star, as well as with the VLT/SPHERE and VLT/NaCo nondetection.

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A dusty benchmark brown dwarf near the ice line of HD 72946

Astronomy and Astrophysics ◽

10.1051/0004-6361/201937134 ◽

2019 ◽

Vol 633 ◽

pp. L2 ◽

Cited By ~ 4

Author(s):

A.-L. Maire ◽

J.-L. Baudino ◽

S. Desidera ◽

S. Messina ◽

W. Brandner ◽

...

Keyword(s):

Proper Motion ◽

Major Axis ◽

High Contrast ◽

Brown Dwarf ◽

Contrast Imaging ◽

Semi Major Axis ◽

Dynamical Mass ◽

High Contrast Imaging ◽

Solar Type ◽

Solar Type Star

Context. HD 72946 is a bright and nearby solar-type star hosting a low-mass companion at long period (P ∼ 16 yr) detected with the radial velocity (RV) method. The companion has a minimum mass of 60.4 ± 2.2 MJ and might be a brown dwarf. Its expected semi-major axis of ∼243 mas makes it a suitable target for further characterization with high-contrast imaging, in particular to measure its inclination, mass, and spectrum and thus definitely establish its substellar nature. Aims. We aim to further characterize the orbit, atmosphere, and physical nature of HD 72946B. Methods. We present high-contrast imaging data in the near-infrared with the Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) instrument. We also use proper motion measurements of the star from HIPPARCOS and Gaia. Results. The SPHERE data reveal a point source with a contrast of ∼9 mag at a projected separation of ∼235 mas. No other point sources are detected in the field of view. By jointly fitting the RV, imaging, and proper motion data, we constrain all the orbital parameters of HD 72946B and assess a dynamical mass of 72.4 ± 1.6 MJ and a semi-major axis of 6.456.45+0.08−0.07 au. Empirical comparison of its SPHERE spectrum to template dwarfs indicates a spectral type of L5.0 ± 1.5. The J–H3 color is close to the expectations of the DUSTY models and suggests a cloudy atmosphere. Comparison with atmospheric models of the spectrophotometry suggests an effective temperature of ∼1700 K. The bolometric luminosity (log(L/L⊙) = −4.11 ± 0.10 dex) and dynamical mass of HD 72946B are more compatible with evolutionary models for an age range of ∼0.9−3 Gyr. The formation mechanism of the companion is currently unclear as the object appears slightly away from the bulk of model predictions. HD 72946B is currently the closest benchmark brown dwarf companion to a solar-type star with imaging, RV, and proper motion measurements.

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A possible dividing line between massive planets and brown-dwarf companions

Proceedings of the International Astronomical Union ◽

10.1017/s1743921311020047 ◽

2010 ◽

Vol 6 (S276) ◽

pp. 117-120 ◽

Cited By ~ 5

Author(s):

Johannes Sahlmann ◽

Damien Ségransan ◽

Didier Queloz ◽

Stéphane Udry

Keyword(s):

Radial Velocity ◽

Formation Process ◽

Brown Dwarfs ◽

Mass Range ◽

Velocity Measurements ◽

Brown Dwarf ◽

The One ◽

The Individual ◽

Dividing Line

AbstractBrown dwarfs are intermediate objects between planets and stars. The lower end of the brown-dwarf mass range overlaps with the one of massive planets and therefore the distinction between planets and brown-dwarf companions may require to trace the individual formation process. We present results on new potential brown-dwarf companions of Sun-like stars, which were discovered using CORALIE radial-velocity measurements. By combining the spectroscopic orbits and Hipparcos astrometric measurements, we have determined the orbit inclinations and therefore the companion masses for many of these systems. This has revealed a mass range between 25 and 45 Jupiter masses almost void of objects, suggesting a possible dividing line between massive planets and sub-stellar companions.

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Direct imaging of an ultracool substellar companion to the exoplanet host star HD 4113 A

Astronomy and Astrophysics ◽

10.1051/0004-6361/201630136 ◽

2018 ◽

Vol 614 ◽

pp. A16 ◽

Cited By ~ 16

Author(s):

A. Cheetham ◽

D. Ségransan ◽

S. Peretti ◽

J.-B. Delisle ◽

J. Hagelberg ◽

...

Keyword(s):

Giant Planet ◽

Radial Velocities ◽

Physical Parameters ◽

Imaging Data ◽

Brown Dwarf ◽

Contrast Imaging ◽

Direct Imaging ◽

Dynamical Mass ◽

Methane Absorption ◽

Mass Estimate

Using high-contrast imaging with the SPHERE instrument at the Very Large Telescope (VLT), we report the first images of a cold brown dwarf companion to the exoplanet host star HD 4113A. The brown dwarf HD 4113C is part of a complex dynamical system consisting of a giant planet, a stellar host, and a known wide M-dwarf companion. Its separation of 535 ± 3 mas and H-band contrast of 13.35 ± 0.10 mag correspond to a projected separation of 22 AU and an isochronal mass estimate of 36 ± 5 MJ based on COND models. The companion shows strong methane absorption, and through fitting an atmosphere model, we estimate a surface gravity of logg = 5 and an effective temperature of ~500–600 K. A comparison of its spectrum with observed T dwarfs indicates a late-T spectral type, with a T9 object providing the best match. By combining the observed astrometry from the imaging data with 27 years of radial velocities, we use orbital fitting to constrain its orbital and physical parameters, as well as update those of the planet HD 4113A b, discovered by previous radial velocity measurements. The data suggest a dynamical mass of 66−4+5 MJ and moderate eccentricity of 0.44−0.07+0.08 for the brown dwarf. This mass estimate appears to contradict the isochronal estimate and that of objects with similar temperatures, which may be caused by the newly detected object being an unresolved binary brown dwarf system or the presence of an additional object in the system. Through dynamical simulations, we show that the planet may undergo strong Lidov-Kozai cycles, raising the possibility that it formed on a quasi-circular orbit and gained its currently observed high eccentricity (e ~ 0.9) through interactions with the brown dwarf. Follow-up observations combining radial velocities, direct imaging, and Gaia astrometry will be crucial to precisely constrain the dynamical mass of the brown dwarf and allow for an in-depth comparison with evolutionary and atmosphere models.

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The Gemini NICI Planet-Finding Campaign: The Frequency of Giant Planets around Young B and A Stars

Proceedings of the International Astronomical Union ◽

10.1017/s1743921313007874 ◽

2013 ◽

Vol 8 (S299) ◽

pp. 60-61

Author(s):

Eric L. Nielsen ◽

Michael C. Liu ◽

Zahed Wahhaj ◽

Beth A. Biller ◽

Thomas L. Hayward ◽

...

Keyword(s):

Brown Dwarfs ◽

Giant Planets ◽

High Mass ◽

High Contrast ◽

Brown Dwarf ◽

Contrast Imaging ◽

High Contrast Imaging ◽

Null Result ◽

Upper Limits

AbstractWe have carried out high contrast imaging of 70 young, nearby B and A stars to search for brown dwarf and planetary companions as part of the Gemini NICI Planet-Finding Campaign. Our survey represents the largest, deepest survey for planets around high-mass stars (≈1.5–2.5 M⊙) conducted to date and includes the planet hosts β Pic and Fomalhaut. Despite detecting two new brown dwarfs, our observations did not detect new planets around our target stars, and we present upper limits on the fraction of high-mass stars that can host giant planets that are consistent with our null result.

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Unveiling the β Pictoris system, coupling high contrast imaging, interferometric, and radial velocity data

Astronomy and Astrophysics ◽

10.1051/0004-6361/202038823 ◽

2020 ◽

Vol 642 ◽

pp. A18

Author(s):

A. M. Lagrange ◽

P. Rubini ◽

M. Nowak ◽

S. Lacour ◽

A. Grandjean ◽

...

Keyword(s):

Radial Velocity ◽

Gravity Data ◽

Giant Planet ◽

Base Line ◽

High Contrast ◽

Imaging Data ◽

Contrast Imaging ◽

Orbital Parameters ◽

High Contrast Imaging ◽

The Impact

Context. The nearby and young β Pictoris system hosts a well resolved disk, a directly imaged massive giant planet orbiting at ≃9 au, as well as an inner planet orbiting at ≃2.7 au, which was recently detected through radial velocity (RV). As such, it offers several unique opportunities for detailed studies of planetary system formation and early evolution. Aims. We aim to further constrain the orbital and physical properties of β Pictoris b and c using a combination of high contrast imaging, long base-line interferometry, and RV data. We also predict the closest approaches or the transit times of both planets, and we constrain the presence of additional planets in the system. Methods. We obtained six additional epochs of SPHERE data, six additional epochs of GRAVITY data, and five additional epochs of RV data. We combined these various types of data in a single Markov-chain Monte Carlo analysis to constrain the orbital parameters and masses of the two planets simultaneously. The analysis takes into account the gravitational influence of both planets on the star and hence their relative astrometry. Secondly, we used the RV and high contrast imaging data to derive the probabilities of presence of additional planets throughout the disk, and we tested the impact of absolute astrometry. Results. The orbital properties of both planets are constrained with a semi-major axis of 9.8 ± 0.4 au and 2.7 ± 0.02 au for b and c, respectively, and eccentricities of 0.09 ± 0.1 and 0.27 ± 0.07, assuming the HIPPARCOS distance. We note that despite these low fitting error bars, the eccentricity of β Pictoris c might still be over-estimated. If no prior is provided on the mass of β Pictoris b, we obtain a very low value that is inconsistent with what is derived from brightness-mass models. When we set an evolutionary model motivated prior to the mass of β Pictoris b, we find a solution in the 10–11 MJup range. Conversely, β Pictoris c’s mass is well constrained, at 7.8 ± 0.4 MJup, assuming both planets are on coplanar orbits. These values depend on the assumptions on the distance of the β Pictoris system. The absolute astrometry HIPPARCOS-Gaia data are consistent with the solutions presented here at the 2σ level, but these solutions are fully driven by the relative astrometry plus RV data. Finally, we derive unprecedented limits on the presence of additional planets in the disk. We can now exclude the presence of planets that are more massive than about 2.5 MJup closer than 3 au, and more massive than 3.5 MJup between 3 and 7.5 au. Beyond 7.5 au, we exclude the presence of planets that are more massive than 1–2 MJup. Conclusions. Combining relative astrometry and RVs allows one to precisely constrain the orbital parameters of both planets and to give lower limits to potential additional planets throughout the disk. The mass of β Pictoris c is also well constrained, while additional RV data with appropriate observing strategies are required to properly constrain the mass of β Pictoris b.

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A Deep Large area Search for Low Luminosity Stars

Highlights of Astronomy ◽

10.1017/s1539299600021675 ◽

1998 ◽

Vol 11 (1) ◽

pp. 435-435

Author(s):

Hugh R.A. Jones ◽

Mike R.S. Hawkins

Keyword(s):

Spectral Type ◽

Low Temperatures ◽

Current Model ◽

Brown Dwarfs ◽

Evolutionary Models ◽

Spectral Indices ◽

Late Type ◽

Brown Dwarf ◽

Large Area ◽

M Dwarfs

In a recent survey for faint red stars from a digital stack of Schmidt plates a number of candidate objects were identified. Parallax’s for three of these objects have been reported showing them to have luminosities which interpreted within the available evolutionary models indicate them to be good brown dwarf candidates. Here we examine spectra of these objects and others from the plate stack. Using standard spectral indices we find that for a given spectral type their spectra are more consistent with the Pleiades brown dwarfs (PPL 15, Teide 1 and Calar 3) than with standard late-type M dwarfs. Our interpretation is that this is due to their selection by RF IN colours which at values > 3 preferentially selects objects with relatively low gravities. For late-type M dwarfs and brown dwarfs low gravities are expected to be a reliable indication of youth. We also notice that the stack objects generally have strong FeH absorption for their spectral type. Current model atmospheres suggest that FeH strongly increases in strength toward lower metallicities and lower temperatures. We believe that this is not consistent with the available observational evidence from late-type M dwarfs. It is possible that solid Fe is forming inthe low temperature atmospheres relatively depleting FeH strengths toward lower temperatures. We find some evidence that for dwarfs at low temperatures dust formation is less prevalent in lower gravity objects suggesting that dwarfs at low temperatures stronger FeH may be an indication of youth. In addition to the spectral evidence the three stack objects whose parallax’s have been measured show small tangential velocities which is a further indication of youth.

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PynPoint: a modular pipeline architecture for processing and analysis of high-contrast imaging data

Astronomy and Astrophysics ◽

10.1051/0004-6361/201834136 ◽

2019 ◽

Vol 621 ◽

pp. A59 ◽

Cited By ~ 15

Author(s):

T. Stolker ◽

M. J. Bonse ◽

S. P. Quanz ◽

A. Amara ◽

G. Cugno ◽

...

Keyword(s):

Data Reduction ◽

Direct Detection ◽

Principal Component ◽

Monte Carlo Analysis ◽

Data Sets ◽

High Contrast ◽

Imaging Data ◽

Pipeline Architecture ◽

Contrast Imaging ◽

High Contrast Imaging

Context. The direct detection and characterization of planetary and substellar companions at small angular separations is a rapidly advancing field. Dedicated high-contrast imaging instruments deliver unprecedented sensitivity, enabling detailed insights into the atmospheres of young low-mass companions. In addition, improvements in data reduction and point spread function (PSF)-subtraction algorithms are equally relevant for maximizing the scientific yield, both from new and archival data sets. Aims. We aim at developing a generic and modular data-reduction pipeline for processing and analysis of high-contrast imaging data obtained with pupil-stabilized observations. The package should be scalable and robust for future implementations and particularly suitable for the 3–5 μm wavelength range where typically thousands of frames have to be processed and an accurate subtraction of the thermal background emission is critical. Methods. PynPoint is written in Python 2.7 and applies various image-processing techniques, as well as statistical tools for analyzing the data, building on open-source Python packages. The current version of PynPoint has evolved from an earlier version that was developed as a PSF-subtraction tool based on principal component analysis (PCA). Results. The architecture of PynPoint has been redesigned with the core functionalities decoupled from the pipeline modules. Modules have been implemented for dedicated processing and analysis steps, including background subtraction, frame registration, PSF subtraction, photometric and astrometric measurements, and estimation of detection limits. The pipeline package enables end-to-end data reduction of pupil-stabilized data and supports classical dithering and coronagraphic data sets. As an example, we processed archival VLT/NACO L′ and M′ data of β Pic b and reassessed the brightness and position of the planet with a Markov chain Monte Carlo analysis; we also provide a derivation of the photometric error budget.

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