scholarly journals HST/WFC3 Complete Phase-resolved Spectroscopy of White-dwarf-brown-dwarf Binaries WD 0137 and EPIC 2122

2021 ◽  
Vol 163 (1) ◽  
pp. 17
Author(s):  
Yifan Zhou ◽  
Dániel Apai ◽  
Xianyu Tan ◽  
Joshua D. Lothringer ◽  
Ben W. P. Lew ◽  
...  
Keyword(s):  
Heat Transfer ◽  
White Dwarf ◽  
Hubble Space Telescope ◽  
Hot Spot ◽  
Brown Dwarfs ◽  
Wide Field ◽  
Brown Dwarf ◽  
Object A ◽  
M Phase ◽  
Night Flux

Abstract Brown dwarfs in close-in orbits around white dwarfs offer an excellent opportunity to investigate properties of fast-rotating, tidally locked, and highly irradiated atmospheres. We present Hubble Space Telescope Wide Field Camera 3 G141 phase-resolved observations of two brown-dwarf-white-dwarf binaries: WD 0137-349 and EPIC 212235321. Their 1.1–1.7 μm phase curves demonstrate rotational modulations with semi-amplitudes of 5.27% ± 0.02% and 29.1% ± 0.1%; both can be fit well by multi-order Fourier series models. The high-order Fourier components have the same phase as the first-order and are likely caused by hot spots located at the substellar points, suggesting inefficient day/night heat transfer. Both brown dwarfs’ phase-resolved spectra can be accurately represented by linear combinations of their respective day- and nightside spectra. Fitting the irradiated brown dwarf model grids to the dayside spectra require a filling factor of ∼50%, further supporting a hot spot dominating the dayside emission. The nightside spectrum of WD 0137-349B is fit reasonably well by non-irradiated substellar models, and the one of EPIC 21223521B can be approximated by a Planck function. We find strong spectral variations in the brown dwarfs’ day/night flux and brightness temperature contrasts, highlighting the limitations of band-integrated measurements in probing heat transfer in irradiated objects. On the color–magnitude diagram, WD 0137-349B evolves along a cloudless model track connecting the early-L and mid-T spectral types, suggesting that clouds and disequilibrium chemistry have a negligible effect on this object. A full interpretation of these high-quality phase-resolved spectra calls for new models that couple atmospheric circulation and radiative transfer under high-irradiation conditions.

scholarly journals Considerations for atmospheric retrieval of high-precision brown dwarf spectra

2020 ◽  
Vol 497 (4) ◽  
pp. 5136-5154
Author(s):  
Anjali A A Piette ◽  
Nikku Madhusudhan
Keyword(s):  
High Precision ◽  
Thermal Emission ◽  
Simulated Data ◽  
Brown Dwarfs ◽  
High Signal ◽  
Temperature Structure ◽  
Wide Field ◽  
Brown Dwarf ◽  
Data Set ◽  
Stellar Objects

ABSTRACT Isolated brown dwarfs provide remarkable laboratories for understanding atmospheric physics in the low-irradiation regime, and can be observed more precisely than exoplanets. As such, they provide a glimpse into the future of high-signal-to-noise ratio (SNR) observations of exoplanets. In this work, we investigate several new considerations that are important for atmospheric retrievals of high-quality thermal emission spectra of sub-stellar objects. We pursue this using an adaptation of the h y dra atmospheric retrieval code. We propose a parametric pressure–temperature (P–T) profile for brown dwarfs consisting of multiple atmospheric layers, parametrized by the temperature change across each layer. This model allows the steep temperature gradient of brown dwarf atmospheres to be accurately retrieved while avoiding commonly encountered numerical artefacts. The P–T model is especially flexible in the photosphere, which can reach a few tens of bar for T-dwarfs. We demonstrate an approach to include model uncertainties in the retrieval, focusing on uncertainties introduced by finite spectral and vertical resolution in the atmospheric model used for retrieval (∼8 per cent in the present case). We validate our retrieval framework by applying it to a simulated data set and then apply it to the HST/WFC3 (Hubble Space Telescope’s Wide-Field Camera 3) spectrum of the T-dwarf 2MASS J2339+1352. We retrieve sub-solar abundances of H2O and CH4 in the object at ∼0.1 dex precision. Additionally, we constrain the temperature structure to within ∼100 K in the photosphere. Our results demonstrate the promise of high-SNR spectra to provide high-precision abundance estimates of sub-stellar objects.

scholarly journals Environmental effects on the ionisation of brown dwarf atmospheres

2018 ◽  
Vol 618 ◽  
pp. A107 ◽  
Author(s):  
M. I. Rodríguez-Barrera ◽  
Ch. Helling ◽  
K. Wood
Keyword(s):  
White Dwarf ◽  
Binary Systems ◽  
Brown Dwarfs ◽  
High Energy ◽  
Radiation Environment ◽  
Brown Dwarf ◽  
Star Forming ◽  
Star Forming Regions ◽  
Lyman Continuum ◽  
Low Mass

Context. Brown dwarfs emit bursts of Hα, white-light flares, and show radio flares and quiescent radio emission. They are suggested to form aurorae, similar to planets in the solar system, but much more energetic. All these processes require a source gas with an appropriate degree of ionisation, which, so far, is mostly postulated to be sufficient. Aims. We aim to demonstrate that the Galactic environment influences atmospheric ionisation, and that it hence amplifies or enables the magnetic coupling of the atmospheres of ultra-cool objects, like brown dwarfs and free-floating planets. Methods. We build on our previous work on thermal ionisation of ultra-cool atmospheres and explore the effect of environmental high-energy radiation on the degree of ionisation in the atmosphere. We consider the effect of photoionisation by Lyman-continuum radiation in three different environments: in the interstellar radiation field (ISRF), O and B stars in star-forming regions, and in white dwarf companions in binary systems. We apply our Monte Carlo radiation transfer code to investigate the effect of Lyman-continuum photoionisation for prescribed atmosphere structures for very low-mass objects. Results. The external radiation environment plays an important role for the atmospheric ionisation of very low-mass, ultra-cool objects. Lyman-continuum irradiation greatly increases the level of ionisation in the uppermost atmospheric regions. Our results suggest that a shell of an almost fully ionised atmospheric gas emerges for brown dwarfs in star-forming regions and brown dwarfs in white dwarf binary systems. As a consequence, brown dwarf atmospheres can be magnetically coupled, which is the presumption for chromospheric heating to occur and for aurorae to emerge. First tests for assumed chromosphere-like temperature values suggest that the resulting free-free X-ray luminosities are comparable with those observed from non-accreting brown dwarfs in star-forming regions.

A Search for Brown Dwarfs in the Alpha Persei Cluster

2003 ◽  
Vol 211 ◽  
pp. 179-180
Author(s):  
Nicolas Lodieu ◽  
Mark McCaughrean ◽  
Jérôme Bouvier ◽  
David Barrado y Navascués ◽  
John R. Stauffer
Keyword(s):  
Near Infrared ◽  
Open Cluster ◽  
Brown Dwarfs ◽  
Wide Field ◽  
Brown Dwarf ◽  
Young Open Cluster ◽  
Low Mass ◽  
Alpha Persei ◽  
Calar Alto ◽  
Infrared Survey

We present preliminary results from a deep near-infrared survey of a ~ 1 square degree area in the young open cluster Alpha Persei using the wide-field Omega-Prime camera on the Calar Alto 3.5m telescope, yielding a list of new low-mass cluster members, including brown dwarf candidates.

scholarly journals NLTT5306B: an inflated, weakly irradiated brown dwarf

2020 ◽  
Vol 499 (4) ◽  
pp. 5318-5324
Author(s):  
S L Casewell ◽  
J Debes ◽  
I P Braker ◽  
M C Cushing ◽  
G Mace ◽  
...  
Keyword(s):  
Effective Temperature ◽  
White Dwarf ◽  
Near Infrared ◽  
Brown Dwarfs ◽  
Magnetic Interactions ◽  
Brown Dwarf ◽  
Primary Star ◽  
Brightness Temperatures ◽  
Night Side ◽  
Low Mass

ABSTRACT We present Spitzer observations at 3.6 and 4.5 µm and a near-infrared IRTF SpeX spectrum of the irradiated brown dwarf NLTT5306B. We determine that the brown dwarf has a spectral type of L5 and is likely inflated, despite the low effective temperature of the white dwarf primary star. We calculate brightness temperatures in the Spitzer wavebands for both the model radius, and Roche Lobe radius of the brown dwarf, and conclude that there is very little day–night side temperature difference. We discuss various mechanisms by which NLTT5306B may be inflated, and determine that while low-mass brown dwarfs (M < 35 MJup) are easily inflated by irradiation from their host star, very few higher mass brown dwarfs are inflated. The higher mass brown dwarfs that are inflated may be inflated by magnetic interactions or may have thicker clouds.

scholarly journals The Search for Brown Dwarfs around White Dwarfs

2003 ◽  
Vol 211 ◽  
pp. 289-292 ◽  
Author(s):  
J. Farihi ◽  
E. E. Becklin ◽  
B. Zuckerman
Keyword(s):  
Spectral Type ◽  
White Dwarf ◽  
Proper Motion ◽  
White Dwarfs ◽  
Near Field ◽  
Brown Dwarfs ◽  
Wide Field ◽  
M Dwarfs ◽  
Recent Phase ◽  
Motion Search

The infrared search for substellar companions to nearby white dwarfs has been going on for a little more than a decade. The most recent phase has been a wide field proper motion search carried out primarily at Steward Observatory, where we are complete down to J = 18. Earlier phases included near field searches at the IRTF and Keck Observatory. In the last year we have discovered ten previously unrecognized faint proper motion companions. Of the recent discoveries, most are white dwarfs and a few M dwarfs. GD165B, discovered in 1988 as part of our program, is still the only known companion to a white dwarf with spectral type later than M.

scholarly journals Brown dwarf census with the Dark Energy Survey year 3 data and the thin disc scale height of early L types

2019 ◽  
Vol 489 (4) ◽  
pp. 5301-5325 ◽  
Author(s):  
A Carnero Rosell ◽  
B Santiago ◽  
M dal Ponte ◽  
B Burningham ◽  
L N da Costa ◽  
...  
Keyword(s):  
Dark Energy ◽  
Structural Parameters ◽  
Brown Dwarfs ◽  
Scale Height ◽  
Wide Field ◽  
Brown Dwarf ◽  
Thin Disc ◽  
Dark Energy Survey ◽  
Significant Difference ◽  
Energy Survey

ABSTRACT In this paper we present a catalogue of 11 745 brown dwarfs with spectral types ranging from L0 to T9, photometrically classified using data from the Dark Energy Survey (DES) year 3 release matched to the Vista Hemisphere Survey (VHS) DR3 and Wide-field Infrared Survey Explorer (WISE) data, covering ≈2400 deg2 up to iAB = 22. The classification method follows the same phototype method previously applied to SDSS-UKIDSS-WISE data. The most significant difference comes from the use of DES data instead of SDSS, which allow us to classify almost an order of magnitude more brown dwarfs than any previous search and reaching distances beyond 400 pc for the earliest types. Next, we also present and validate the GalmodBD simulation, which produces brown dwarf number counts as a function of structural parameters with realistic photometric properties of a given survey. We use this simulation to estimate the completeness and purity of our photometric LT catalogue down to iAB = 22, as well as to compare to the observed number of LT types. We put constraints on the thin disc scale height for the early L (L0–L3) population to be around 450 pc, in agreement with previous findings. For completeness, we also publish in a separate table a catalogue of 20 863 M dwarfs that passed our colour cut with spectral types greater than M6. Both the LT and the late M catalogues are found at DES release page https://des.ncsa.illinois.edu/releases/other/y3-mlt.

scholarly journals Extending Gaia  DR2 with HST  narrow-field astrometry – II. Refining the method on WISE J163940.83−684738.6★

2020 ◽  
Vol 494 (2) ◽  
pp. 2068-2075
Author(s):  
L R Bedin ◽  
C Fontanive
Keyword(s):  
High Precision ◽  
Reference System ◽  
Hubble Space Telescope ◽  
High Accuracy ◽  
Test Case ◽  
Wide Field ◽  
Brown Dwarf ◽  
Space Telescope ◽  
Infra Red ◽  
Gaia Dr2

ABSTRACT In the second paper of this series, we perfected our method of linking high-precision Hubble Space Telescope astrometry to the high-accuracy Gaia DR2 absolute reference system to overcome the limitations of relative astrometry with narrow-field cameras. Our test case here is the Y brown dwarf WISE  J163940.83−684738.6, observed at different epochs spread over a 6-yr time baseline with the Infra-Red channel of the Wide Field Camera 3. We derived significantly improved astrometric parameters compared to previous determinations, finding (μαcos δ, μδ, ϖ) = (577.21 ± 0.24 mas yr−1, −3108.39 ± 0.27 mas yr−1, 210.4 ± 1.8 mas). In particular, our derived absolute parallax (ϖ ) corresponds to a distance of 4.75 ± 0.05 pc for the faint ultracool dwarf.

scholarly journals Mapping the Pressure-dependent Day–Night Temperature Contrast of a Strongly Irradiated Atmosphere with HST Spectroscopic Phase Curve

2021 ◽  
Vol 163 (1) ◽  
pp. 8
Author(s):  
Ben W. P. Lew ◽  
Dániel Apai ◽  
Yifan Zhou ◽  
Mark Marley ◽  
L. C. Mayorga ◽  
...  
Keyword(s):  
White Dwarf ◽  
Near Infrared ◽  
Brown Dwarfs ◽  
Phase Curve ◽  
Brown Dwarf ◽  
Night Temperature ◽  
Flux Variation ◽  
Hot Jupiters ◽  
Temperature Contrast ◽  
Hot Jupiter

Abstract Many brown dwarfs are on ultrashort-period and tidally locked orbits around white dwarf hosts. Because of these small orbital separations, the brown dwarfs are irradiated at levels similar to hot Jupiters. Yet, they are easier to observe than hot Jupiters because white dwarfs are fainter than main-sequence stars at near-infrared wavelengths. Irradiated brown dwarfs are, therefore, ideal hot Jupiter analogs for studying the atmospheric response under strong irradiation and fast rotation. We present the 1.1–1.67 μm spectroscopic phase curve of the irradiated brown dwarf (SDSS1411-B) in the SDSS J141126.20 + 200911.1 brown dwarf–white dwarf binary with the near-infrared G141 grism of the Hubble Space Telescope Wide Field Camera 3. SDSS1411-B is a 50M Jup brown dwarf with an irradiation temperature of 1300 K and has an orbital period of 2.02864 hr. Our best-fit model suggests a phase-curve amplitude of 1.4% and places an upper limit of 11° for the phase offset from the secondary eclipse. After fitting the white dwarf spectrum, we extract the phase-resolved brown dwarf emission spectra. We report a highly wavelength-dependent day–night spectral variation, with a water-band flux variation of about 360% ± 70% and a comparatively small J-band flux variation of 37% ± 2%. By combining the atmospheric modeling results and the day–night brightness temperature variations, we derive a pressure-dependent temperature contrast. We discuss the difference in the spectral features of SDSS1411-B and hot Jupiter WASP-43b, as well as the lower-than-predicted day–night temperature contrast of J4111-BD. Our study provides the high-precision observational constraints on the atmospheric structures of an irradiated brown dwarf at different orbital phases.

Recent Results from the High Speed Photometer

1993 ◽  
Vol 136 ◽  
pp. 356-357
Author(s):  
M. Taylor ◽  
R.C. Bless ◽  
M. Nelson ◽  
J. Percival ◽  
A. Bosh ◽  
...  
Keyword(s):  
Light Curve ◽  
White Dwarf ◽  
High Speed ◽  
Hubble Space Telescope ◽  
Hot Spot ◽  
Main Pulse ◽  
Physical Parameters ◽  
Stellar Photometry ◽  
Infrared Wavelengths ◽  
Ultraviolet Observations

AbstractOne of the first stellar photometry programs completed with the High Speed Photometer (HSP) on the Hubble Space Telescope (HST) was visual and ultraviolet observations of the Crab pulsar. We obtained continuous observations on four consecutive days using a visual filter (4000 - 7000 Å) and an additional observation, approximately two months later, using an ultraviolet filter (1600 - 3000 Å). Each observation has a time resolution of 10.7 μsec and spans approximately 30 minutes in duration. In addition to the observations made with the HSP, contemporaneous UBVR observations were also made at Jodrell Bank and McDonald Observatory. Some of the more prominent results include the following: 1) the main pulse arrival time is the same in the UV as it is in the optical and the radio regions of the spectrum, 2) there is essentially no difference in the shape of the optical pulse from one observation to the next, 3) the “flatness” of the peak of the main pulse suggests that the main pulse has been resolved in time, and 4) in accordance with the trend of observations from the radio to infrared wavelengths, the main pulse is slightly narrower in the UV than in the optical.A second HSP science observing program was a long-term program to monitor the eclipsing dwarf nova, Z Chamaeleontis (Porb = 107 minutes). We obtained a total of 42 observations of Z Cha in the UV (1120 - 1580 Å) each with a duration of approximately 45 minutes and separated by approximately three days. Although the majority of the observations cover the eclipse of the white dwarf and hot spot, a few observations were obtained outside-of-eclipse in order to obtain the complete light curve. During the course of this program, Z Cha underwent two “normal” outbursts in which the shape of the light curve changed dramatically. We will present a comparison of the light curve in quiescence with that during a “normal” outburst and quantify such geometrical and physical parameters as temperature and size of the white dwarf, hot spot, and accretion disk.

scholarly journals The Brown Dwarf Deficit in Taurus: Evidence for a Non-Universal IMF

2003 ◽  
Vol 211 ◽  
pp. 81-82 ◽  
Author(s):  
César Briceño ◽  
Kevin L. Luhman ◽  
Lee Hartmann ◽  
John R. Stauffer ◽  
J. Davy Kirkpatrick
Keyword(s):  
Brown Dwarfs ◽  
Mass Function ◽  
Initial Mass Function ◽  
Wide Field ◽  
Low Density ◽  
Brown Dwarf ◽  
New Members ◽  
Star Forming ◽  
Field Imaging ◽  
Wide Field Imaging

We present the results of a deep, optical/IR wide field imaging survey of selected fields in the nearby (d~ 140 pc) Taurus star-forming region. We report the discovery of 9 new members with spectral types M5.75–M9.5. We derive an Initial Mass Function encompassing 54% of the known members in Taurus. Comparison with dense regions like the Trapezium Cluster in Orion shows that Taurus has produced x2 less brown dwarfs. We suggest that the lower frequency of brown dwarfs in Taurus may result from the low-density star-forming environment, leading to larger minimum Jeans masses.

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