Publications (75)
Methane Opacities in T Dwarf Atmospheres
D. Homeier, P. H. Hauschildt, F. Allard
We present the current status of PHOENIX model atmospheres for dwarfs of the spectral type T, typical for older field brown dwarfs and low-mass brown dwarfs. The results are based…
Fifteen new T dwarfs discovered in the UKIDSS Large Area Survey
D. J. Pinfield, B. Burningham, M. Tamura +32
We present the discovery of fifteen new T2.5-T7.5 dwarfs (with estimated distances between ~24-93pc, identified in the first three main data releases of the UKIRT Infrared Deep Sky…
Near-infrared spectroscopic characterisation of Gaia ultra-cool dwarf candidates; Spectral types and peculiarities
T. Ravinet, C. Reylé, N. Lagarde +10
Context: The local census of very low-mass stars and brown dwarfs is crucial to improving our understanding of the stellar-substellar transition and their formation history. These…
CFBDSIR 2149-0403: young isolated planetary-mass object or high-metallicity low-mass brown dwarf??
P. Delorme, T. Dupuy, J. Gagné +12
We conducted a multi-wavelength, multi-instrument observational characterisation of the candidate free-floating planet CFBDSIR~J214947.2-040308.9, a late T-dwarf with possible low-…
Spectral synthesis of circumstellar disks - application to white dwarf debris disks
S. D. Huegelmeyer, S. Dreizler, D. Homeier +1
Gas and dust disks are common objects in the universe and can be found around various objects, e.g. young stars, cataclysmic variables, active galactic nuclei, or white dwarfs. The…
Temperature constraints on the coldest brown dwarf known WISE 0855-0714
J. C. BeamÃn, V. D. Ivanov, A. Bayo +10
Context. Nearby isolated planetary mass objects are beginning to be discovered, but their individual properties are poorly constrained because their low surface temperatures and st…
Search for progenitors of supnernovae type Ia with SPY
R. Napiwotzki, N. Christlieb, H. Drechsel +13
We have started a large survey for double degenerate (DD) binaries as potential progenitors of type Ia supernovae with the UVES spectrograph at the ESO VLT (ESO SN Ia Progenitor su…
Near-infrared integral-field spectra of the planet/brown dwarf companion AB Pic b
M. Bonnefoy, G. Chauvin, P. Rojo +5
Chauvin et al. 2005 imaged a co-moving companion at ~260 AU from the young star AB Pic A. Evolutionary models predictions based on J H K photometry of AB Pic b suggested a mass of…
An in-depth spectroscopic examination of molecular bands from 3D hydrodynamical model atmospheres. II. Carbon-enhanced metal-poor 3D model atmospheres
A. J. Gallagher, E. Caffau, P. Bonifacio +4
Context. Tighter constraints on metal-poor stars we observe are needed to better understand the chemical processes of the early Universe. Computing a stellar spectrum in 3D allows…
Progress in Modeling Very Low Mass Stars, Brown Dwarfs, and Planetary Mass Objects
F. Allard, D. Homeier, B. Freytag +2
We review recent advancements in modeling the stellar to substellar transition. The revised molecular opacities, solar oxygen abundances and cloud models allow to reproduce the pho…
Physical and orbital properties of Beta Pictoris b
M. Bonnefoy, G. -D. Marleau, R. Galicher +13
The intermediate-mass star Beta Pictoris is known to be surrounded by a structured edge-on debris disk within which a gas giant planet was discovered orbiting at 8-10 AU. The physi…
Metallicity, temperature, and gravity scales of M subdwarfs
N. Lodieu, F. Allard, C. Rodrigo +5
The aim of the project is to define a metallicity/gravity/temperature scale vs spectral types for metal-poor M dwarfs. We obtained intermediate-resolution ultraviolet (R~3300), opt…
Spectral analyses of eighteen hot H-deficient (pre-) white dwarfs from the Sloan Digital Sky Survey Data Release 4
S. D. Huegelmeyer, S. Dreizler, D. Homeier +4
Context: The Sloan Digital Sky Survey Data Release 4 has provided spectra of several new PG 1159 stars and DO white dwarfs. This increase in known hot H-deficient compact objects s…
A very cool brown dwarf in UKIDSS DR1
S. J. Warren, D. J. Mortlock, S. K. Leggett +21
(abridged) We report the discovery of a very cool brown dwarf, ULAS J003402.77-005206.7 (ULAS J0034-00), identified in UKIDSS DR1. We provide optical, near-infrared, and mid-infrar…
High-resolution UVES/VLT spectra of white dwarfs observed for the ESO SN Ia Progenitor Survey. III. DA white dwarfs
D. Koester, B. Voss, R. Napiwotzki +5
The ESO Supernova Ia Progenitor Survey (SPY) took high-resolution spectra of more than 1000 white dwarfs and pre-white dwarfs. About two thirds of the stars observed are hydrogen-d…
Close binary EHB stars from SPY
R. Napiwotzki, C. A. Karl, T. Lisker +5
We present the results of a radial velocity (RV) survey of 46 subdwarf B (sdB) and 23 helium-rich subdwarf O (He-sdO) stars. We detected 18 (39%) new sdB binary systems, but only o…
CFBDSIR2149-0403: a 4-7 Jupiter-mass free-floating planet in the young moving group AB Doradus ?
P. Delorme, J. Gagné, L. Malo +7
Using the CFBDSIR wide field survey for brown dwarfs, we identified CFBDSIRJ214947.2-040308.9, a late T dwarf with atypically red J-Ks colour. We obtained an X-Shooter spectra, wit…
A library of near-infrared integral field spectra of young M-L dwarfs
M. Bonnefoy, G. Chauvin, A. -M. Lagrange +5
We present a library of near-infrared (1.1-2.45 microns) medium-resolution (R~1500-2000) integral field spectra of 15 young M6-L0 dwarfs, composed of companions with known ages and…
Detection and characterisation of two VLM binaries: LP 1033-31 and LP 877-72
Subhajeet Karmakar, A. S. Rajpurohit, F. Allard +1
Using the high-resolution near-infrared adaptive optics imaging from the NaCo instrument at the Very Large Telescope, we report the discovery of a new binary companion to the M-dwa…
Search for double degenerate progenitors of supernovae type Ia with SPY
R. Napiwotzki, H. Drechsel, U. Heber +13
We report on a large survey for double degenerate (DD) binaries as potential progenitors of type Ia supernovae with the UVES spectrograph at the ESO VLT (ESO SN Ia Progenitor surve…
Seventy six T dwarfs from the UKIDSS LAS: benchmarks, kinematics and an updated space density
Ben Burningham, C. V. Cardoso, L. Smith +34
We report the discovery of 76 new T dwarfs from the UKIDSS Large Area Survey (LAS). Near-infrared broad and narrow-band photometry and spectroscopy are presented for the new object…
New constraints on the formation and settling of dust in the atmospheres of young M and L dwarfs
E. Manjavacas, M. Bonnefoy, J. E. Schlieder +7
We obtained medium-resolution near-infrared spectra of seven young M9.5-L3 dwarfs classified in the optical. We aim to confirm the low surface gravity of the objects in the NIR. We…
Investigation of transit-selected exoplanet candidates from the MACHO survey
S. D. Huegelmeyer, S. Dreizler, D. Homeier +1
Context: Planets outside our solar system transiting their host star, i. e. those with an orbital inclination near 90 degree, are of special interest to derive physical properties…
Radiative transfer in circumstellar disks - I. 1D models for GQ Lupi
S. D. Huegelmeyer, S. Dreizler, P. H. Hauschildt +3
We present a new code for the calculation of the 1D structure and synthetic spectra of accretion disks. The code is an extension of the general purpose stellar atmosphere code PHOE…
The Astropy Project: Building an inclusive, open-science project and status of the v2.0 core package
The Astropy Collaboration, A. M. Price-Whelan, B. M. SipÅcz +134
The Astropy project supports and fosters the development of open-source and openly-developed Python packages that provide commonly-needed functionality to the astronomical communit…
First light of the VLT planet finder SPHERE. IV. Physical and chemical properties of the planets around HR8799
M. Bonnefoy, A. Zurlo, J. L. Baudino +63
The system of four planets around HR8799 offers a unique opportunity to probe the physics and chemistry at play in the atmospheres of self-luminous young (~30 Myr) planets. We rece…
New evolutionary models for pre-main sequence and main sequence low-mass stars down to the hydrogen-burning limit
I. Baraffe, D. Homeier, F. Allard +1
We present new models for low-mass stars down to the hydrogen-burning limit that consistently couple atmosphere and interior structures, thereby superseding the widely used BCAH98…
A comparison of chemistry and dust cloud formation in ultracool dwarf model atmospheres
Ch. Helling, A. Ackerman, F. Allard +8
The atmospheres of substellar objects contain clouds of oxides, iron, silicates, and other refractory condensates. Water clouds are expected in the coolest objects. The opacity of…
The near-infrared spectral energy distribution of β Pictoris b
M. Bonnefoy, A. Boccaletti, A. -M. Lagrange +9
A gas giant planet has previously been directly seen orbiting at 8-10 AU within the debris disk of the ~12 Myr old star β Pictoris. The β Pictoris system offers the rare opportun…
A high resolution spectral atlas of brown dwarfs
A. Reiners, D. Homeier, P. H. Hauschildt +1
We present a UVES/VLT high resolution atlas of three L dwarfs and one T dwarf system, spectral classes at which most of the objects are brown dwarfs. Our atlas covers the optical r…
Exploring the substellar temperature regime down to ~550K
Ben Burningham, D. J. Pinfield, S. K. Leggett +15
We report the discovery of three very late T dwarfs in the UKIRT Infrared Deep Sky Survey (UKIDSS) Third Data Release: ULAS J101721.40+011817.9 (ULAS1017), ULAS J123828.51+095351.3…
Aspects of Multi-Dimensional Modelling of Substellar Atmospheres
Ch. Helling, E. Pedretti, S. Berdyugina +6
Theoretical arguments and observations suggest that the atmospheres of Brown Dwarfs and planets are very dynamic on chemical and on physical time scales. The modelling of such subs…
Primeval very low-mass stars and brown dwarfs. I. Six new L subdwarfs, classification and atmospheric properties
Z. H. Zhang, D. J. Pinfield, M. C. Galvez-Ortiz +10
We have conducted a search for L subdwarf candidates within the photometric catalogues of the UKIRT Infrared Deep Sky Survey and Sloan Digital Sky Survey. Six of our candidates are…
Primeval very low-mass stars and brown dwarfs - III. The halo transitional brown dwarfs
Z. H. Zhang, D. J. Pinfield, M. C. Galvez-Ortiz +11
We report the discovery of an esdL3 subdwarf, ULAS J020858.62+020657.0, and a usdL4.5 subdwarf, ULAS J230711.01+014447.1. They were identified as L subdwarfs by optical spectra obt…
Hot subdwarfs from the ESO Supernova Ia Progenitor Survey - I. Atmospheric parameters and cool companions of sdB stars
T. Lisker, U. Heber, R. Napiwotzki +4
We present the analysis of a high-resolution, high-quality sample of optical spectra for 76 subdwarf B (sdB) stars from the ESO Supernova Ia Progenitor Survey (SPY). Effective temp…
Discovery of the benchmark metal poor T8 dwarf BD+01 2920B
D. J. Pinfield, B. Burningham, N. Lodieu +20
We have searched the WISE first data release for widely separated (<10,000AU) late T dwarf companions to Hipparcos and Gliese stars. We have discovered a new binary system containi…
The ESO supernovae type Ia progenitor survey (SPY)
R. Napiwotzki, C. A. Karl, T. Lisker +13
Close double degenerate binaries are one of the favoured progenitor channels for type Ia supernovae, but it is unclear how many suitable systems there are in the Galaxy. We report…
A dayside thermal inversion in the atmosphere of WASP-19b
A. S. Rajpurohit, F. Allard, D. Homeier +2
Observations of ultra-hot Jupiters indicate the existence of thermal inversion in their atmospheres with day-side temperatures greater than 2200 K. Various physical mechanisms such…
Search for double degenerate progenitors of supernovae type Ia with SPY
R. Napiwotzki, N. Christlieb, H. Drechsel +13
We report on a large survey for double degenerate (DD) binaries as potential progenitors of type Ia supernovae with the UVES spectrograph at the ESO VLT (SN Ia Progenitor surveY -…
A Hubble Space Telescope transit light curve for GJ436b
J. L. Bean, G. F. Benedict, D. Charbonneau +6
We present time series photometry for six partial transits of GJ436b obtained with the Fine Guidance Sensor instrument on the Hubble Space Telescope (HST). Our analysis of these da…
Dynamical masses of M-dwarf binaries in young moving groups: I - The case of TWA 22 and GJ 2060
L. Rodet, M. Bonnefoy, S. Durkan +48
Evolutionary models are widely used to infer the mass of stars, brown dwarfs, and giant planets. Their predictions are thought to be less reliable at young ages ( 200 Myr) and i…
The stellar content of the Hamburg/ESO survey. I. Automated selection of DA white dwarfs
N. Christlieb, L. Wisotzki, D. Reimers +3
We describe automatic procedures for the selection of DA white dwarfs in the Hamburg/ESO objective-prism survey (HES). For this purpose, and the selection of other stellar objects…
On the possibility of detecting extrasolar planets' atmospheres with the Rossiter-McLaughlin-effect
S. Dreizler, A. Reiners, D. Homeier +1
The detection of extrasolar planets' atmospheres requires very demanding observations. For planets that can not be spatially separated from their host stars, i.e. the vast majority…
Monte-Carlo-Simulations of Stochastic Differential Equations at the Example of the Forced Burgers' Equation
D. Homeier, K. Jansen, D. Mesterhazy +1
We investigate the behaviour of stochastic differential equations, especially Burgers' eq., by means of Monte-Carlo-techniques.
Characterization of the gaseous companion κ Andromedae b: New Keck and LBTI high-contrast observations
M. Bonnefoy, T. Currie, G. -D. Marleau +64
We previously reported the direct detection of a low mass companion at a projected separation of 55+-2 AU around the B9 type star κ Andromedae. The properties of the system (mass…
Monte Carlo approach to turbulence
P. Düben, D. Homeier, K. Jansen +2
The behavior of the one-dimensional random-force-driven Burgers equation is investigated in the path integral formalism on a discrete space-time lattice. We show that by means of M…
The very low mass multiple system LHS\,1070 -- a testbed for model atmospheres for the lower end of the main sequence
A. S. Rajpurohit, C. Reyle, M. Schultheis +8
LHS1070 is a nearby multiple system of low mass stars. It is an important source of information for probing the low mass end of the main sequence, down to the hydrogen-burning limi…
The properties of the T8.5p dwarf Ross 458C
Ben Burningham, S. K. Leggett, D. Homeier +12
We present near-infrared photometry and spectroscopy, and warm-Spitzer IRAC photometry of the young very cool T dwarf Ross 458C, which we have typed as T8.5p. By applying the fiduc…
Primeval very low-mass stars and brown dwarfs - IV. New L subdwarfs, Gaia astrometry, population properties, and a blue brown dwarf binary
Z. H. Zhang, M. C. Galvez-Ortiz, D. J. Pinfield +13
We present 27 new L subdwarfs and classify five of them as esdL and 22 as sdL. Our L subdwarf candidates were selected with the UKIRT Infrared Deep Sky Survey and Sloan Digital Sky…
Fingering convection and cloudless models for cool brown dwarf atmospheres
P. Tremblin, D. S. Amundsen, P. Mourier +5
This work aims to improve the current understanding of the atmospheres of brown dwarfs, especially cold ones with spectral type T and Y, whose modeling is a current challenge. Sili…
Multi-modal atmospheric characterization of Pictoris b: Adding high-resolution continuum spectra from GRAVITY
M. Ravet, M. Bonnefoy, G. Chauvin +24
We present the first VLTI/GRAVITY observations at R of Pic b. These four high S/N (20) K-band spectra conserve both the pseudo-continuum and molecular abso…
Using the CIFIST grid of CO5BOLD 3D model atmospheres to study the effects of stellar granulation on photometric colours. I. Grids of 3D corrections in the UBVRI, 2MASS, Hipparcos, Gaia, and SDSS systems
P. Bonifacio, E. Caffau, H. -G. Ludwig +9
The atmospheres of cool stars are temporally and spatially inhomogeneous due to the effects of convection.The influence of this inhomogeneity, referred to as granulation, on colour…
CFBDS J111807-064016: A new L/T transition brown dwarf in a binary system
C. Reylé, P. Delorme, Ã. Artigau +7
Stellar-substellar binary systems are quite rare, and provide interesting benchmarks. They constrain the complex physics of substellar atmospheres, because several physical paramet…
Model Atmospheres From Very Low Mass Stars to Brown Dwarfs
F. Allard, D. Homeier, B. Freytag
Since the discovery of brown dwarfs in 1994, and the discovery of dust cloud formation in the latest Very Low Mass Stars (VLMs) and Brown Dwarfs (BDs) in 1996, the most important c…
The discovery of an M4+T8.5 binary system
Ben Burningham, D. J. Pinfield, S. K. Leggett +17
We report the discovery of a T8.5 dwarf, which is a companion to the M4 dwarf Wolf 940. At a distance of 12.50 (+0.75,-0.67) pc, the angular separation of 32arcsec corresponds to a…
The Properties of the 500 K Dwarf UGPS J072227.51-054031.2, and a Study of the Far-Red Flux of Cold Brown Dwarfs
S. K. Leggett, D. Saumon, M. S. Marley +15
We present i and z photometry for 25 T dwarfs and one L dwarf. Combined with published photometry, the data show that the i - z, z - Y and z - J colors of T dwarfs are very red, an…
The Effective Temperature Scale of M dwarfs
A. S. Rajpurohit, C. Reylé, F. Allard +4
Despite their large number in the Galaxy, M dwarfs remain elusive objects and the modeling of their photospheres has long remained a challenge (molecular opacities, dust cloud form…
Hunting for brown dwarf binaries and testing atmospheric models with X-Shooter
E. Manjavacas, B. Goldman, J. M. Alcalá +7
The determination of the brown dwarf binary fraction may contribute to the understanding of the substellar formation mechanisms. Unresolved brown dwarf binaries may be revealed thr…
High-contrast imaging of Sirius~A with VLT/SPHERE: Looking for giant planets down to one astronomical unit
A. Vigan, C. Gry, G. Salter +4
Sirius has always attracted a lot of scientific interest, especially after the discovery of a companion white dwarf at the end of the 19th century. Very early on, the existence of…
Spectroscopic analysis of sdB stars from the ESO Supernova Ia Progenitor Survey
T. Lisker, U. Heber, R. Napiwotzki +3
We report on the analysis of high-resolution optical spectra for 77 subdwarf B (sdB) stars from the ESO Supernova Ia Progenitor Survey. Effective temperature, surface gravity, and…
First Results from MFOSC-P : Low Resolution Optical Spectroscopy of a Sample of M dwarfs within 100 parsecs
A. S. Rajpurohit, Vipin Kumar, Mudit K. Srivastava +4
Mt. Abu Faint Object Spectrograph and Camera (MFOSC-P) is an in-house developed instrument for Physical Research Laboratory (PRL) 1.2m telescope at Mt. Abu India, commissioned in F…
A new period determination for the close PG1159 binary SDSSJ212531.92-010745.9
S. Schuh, I. Traulsen, T. Nagel +6
Methods to measure masses of PG1159 stars in order to test evolutionary scenarios are currently based on spectroscopic masses or asteroseismological mass determinations. One recent…
A high resolution spectroscopic atlas of M subdwarfs - Effective temperature and metallicity
A. S. Rajpurohit, C. Reyle, F. Allard +4
Context. M subdwarfs are metal poor and cool stars. They are important probes of the old galactic populations. However, they remain elusive due to their low luminosity. Observation…
Peering into the Young Planetary System AB Pic. Atmosphere, Orbit, Obliquity & Second Planetary Candidate
P. Palma-Bifani, G. Chauvin, M. Bonnefoy +24
We aim to revisit the system AB Pic which has a known companion at the exoplanet/ brown-dwarf boundary. We based this study on a rich set of observations to investigate the compani…
Primeval very low-mass stars and brown dwarfs - II. The most metal-poor substellar object
Z. H. Zhang, D. Homeier, D. J. Pinfield +4
SDSS J010448.46+153501.8 has previously been classified as an sdM9.5 subdwarf. However, its very blue colour () suggests a much lower metallicity compared to…
A global cloud map of the nearest known brown dwarf
I. J. M. Crossfield, B. Biller, J. E. Schlieder +9
Brown dwarfs -- substellar bodies more massive than planets but not massive enough to initiate the sustained hydrogen fusion that powers self-luminous stars -- are born hot and slo…
Two new ZZ Ceti pulsators from the HS and HE surveys
R. Silvotti, B. Voss, I. Bruni +4
We report the detection of nonradial g-mode oscillations in the DA white dwarfs HS1039+4112 (B=15.9) and HE1429-0343 (B=15.8) from time-series photometry made at the Loiano 1.5 m t…
Comparison of cloud models for Brown Dwarfs
Ch. Helling, A. Ackerman, F. Allard +8
A test case comparison is presented for different dust cloud model approaches applied in brown dwarfs and giant gas planets. We aim to achieve more transparency in evaluating the u…
Monte Carlo simulations of the randomly forced Burgers equation
P. Düben, D. Homeier, K. Jansen +3
The behaviour of the one--dimensional random--forced Burgers equation is investigated in the path integral formalism, using a discrete space--time lattice. We show that by means of…
Spectral energy distribution of M-subdwarfs: A study of their atmospheric properties
A. S. Rajpurohit, C. Reyle, F. Allard +5
Context. M-type subdwarfs are metal-poor low-mass stars and probe for the old populations in our Galaxy. Accurate knowledge of their atmospheric parameters and especially the compo…
The discovery of the T8.5 dwarf UGPS J0521+3640
Ben Burningham, P. W. Lucas, S. K. Leggett +15
We have carried out a search for late-type T dwarfs in the UKIDSS Galactic Plane Survey 6th Data Release. The search yielded two persuasive candidates, both of which have been conf…
Six New ZZ Ceti Stars from the SPY and the HQS Surveys
B. Voss, D. Koester, R. Ãstensen +3
We report on the discovery of six new ZZ Ceti stars. They were selected as candidates based on preparatory photometric observations of objects from the Hamburg Quasar Survey (HQS),…
Photospheric properties and fundamental parameters of M dwarfs
A. S. Rajpurohit, F. Allard, G. D. C. Teixeira +3
M dwarfs are an important source of information when studying and probing the lower end of the Hertzsprung-Russell (HR) diagram, down to the hydrogen-burning limit. Being the most…
Spectral and atmospheric characterization of 51 Eridani b using VLT/SPHERE
M. Samland, P. Mollière, M. Bonnefoy +37
51 Eridani b is an exoplanet around a young (20 Myr) nearby (29.4 pc) F0-type star, recently discovered by direct imaging. Being only 0.5" away from its host star it is well suited…
Spectral types of planetary host star candidates from OGLE III
S. Dreizler, S. Schuh, D. Homeier
The Optical Gravitational Lensing Experiment project has recently provided the OGLE III list of low-luminosity object transits from campaigns #3 and #4, reporting 40 new objects ex…