HS 2231+2441: an HW Vir system composed of a low-mass white dwarf and a brown dwarf★

ABSTRACT We present an analysis of the second epoch Hubble Space TelescopeWide Field Camera 3 F110W near-infrared (NIR) imaging data of the globular cluster M 4. The new data set suggests that one of the previously suggested four brown dwarf candidates in this cluster is indeed a high-probability cluster member. The position of this object in the NIR colour–magnitude diagrams (CMDs) is in the white dwarf/brown dwarf area. The source is too faint to be a low-mass main-sequence (MS) star, but, according to theoretical considerations, also most likely somewhat too bright to be a bona-fide brown dwarf. Since we know that the source is a cluster member, we determined a new optical magnitude estimate at the position the source should have in the optical image. This new estimate places the source closer to the white dwarf sequence in the optical–NIR CMD and suggests that it might be a very cool (Teff ≤ 4500 K) white dwarf at the bottom of the white dwarf cooling sequence in M 4, or a white dwarf/brown dwarf binary. We cannot entirely exclude the possibility that the source is a very massive, bright brown dwarf, or a very low-mass MS star, however, we conclude that we still have not convincingly detected a brown dwarf in a globular cluster, but we expect to be very close to the start of the brown dwarf cooling sequence in this cluster. We also note that the MS ends at F110W ≈ 22.5 mag in the proper-motion cleaned CMDs, where completeness is still high.

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Environmental effects on the ionisation of brown dwarf atmospheres

Astronomy and Astrophysics ◽

10.1051/0004-6361/201832685 ◽

2018 ◽

Vol 618 ◽

pp. A107 ◽

Cited By ~ 7

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.

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NLTT5306B: an inflated, weakly irradiated brown dwarf

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3184 ◽

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.

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WD1032 + 011, an inflated brown dwarf in an old eclipsing binary with a white dwarf

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa1608 ◽

2020 ◽

Vol 497 (3) ◽

pp. 3571-3580 ◽

Cited By ~ 1

Author(s):

S L Casewell ◽

C Belardi ◽

S G Parsons ◽

S P Littlefair ◽

I P Braker ◽

...

Keyword(s):

Spectral Type ◽

White Dwarf ◽

Light Curves ◽

Brown Dwarf ◽

Eclipsing Binary ◽

The Third ◽

Thick Disc ◽

Low Mass ◽

High Cadence

ABSTRACT We present the discovery of only the third brown dwarf known to eclipse a non-accreting white dwarf. Gaia parallax information and multicolour photometry confirm that the white dwarf is cool (9950 ± 150 K) and has a low mass (0.45 ± 0.05 M⊙), and spectra and light curves suggest the brown dwarf has a mass of 0.067 ± 0.006 M⊙ (70MJup) and a spectral type of L5 ± 1. The kinematics of the system show that the binary is likely to be a member of the thick disc and therefore at least 5-Gyr old. The high-cadence light curves show that the brown dwarf is inflated, making it the first brown dwarf in an eclipsing white dwarf-brown dwarf binary to be so.

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New line profiles of sodium and potassium perturbed by helium for brown dwarf and very cool white dwarf stars

10.1063/1.3026467 ◽

2008 ◽

Author(s):

M. Christova ◽

N. F. Allard ◽

J. F. Kielkopf ◽

D. Homeier ◽

F. Allard ◽

...

Keyword(s):

White Dwarf ◽

Line Profiles ◽

Brown Dwarf ◽

Dwarf Stars ◽

White Dwarf Stars ◽

Sodium And Potassium

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The nature of the close magnetic white dwarf + probable brown dwarf binary SDSS J121209.31+013627.7*

Monthly Notices of the Royal Astronomical Society ◽

10.1111/j.1365-2966.2006.11030.x ◽

2006 ◽

Vol 373 (4) ◽

pp. 1416-1422 ◽

Cited By ~ 32

Author(s):

M. R. Burleigh ◽

T. R. Marsh ◽

B. T. Gänsicke ◽

M. R. Goad ◽

V. S. Dhillon ◽

...

Keyword(s):

White Dwarf ◽

Brown Dwarf

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FURTHER DEFINING SPECTRAL TYPE “Y” AND EXPLORING THE LOW-MASS END OF THE FIELD BROWN DWARF MASS FUNCTION

The Astrophysical Journal ◽

10.1088/0004-637x/753/2/156 ◽

2012 ◽

Vol 753 (2) ◽

pp. 156 ◽

Cited By ~ 227

Author(s):

J. Davy Kirkpatrick ◽

Christopher R. Gelino ◽

Michael C. Cushing ◽

Gregory N. Mace ◽

Roger L. Griffith ◽

...

Keyword(s):

Spectral Type ◽

Mass Function ◽

Brown Dwarf ◽

Low Mass

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Some properties of white-dwarf collapse in low-mass binaries

Astrophysics and Space Science ◽

10.1007/bf00684614 ◽

1983 ◽

Vol 97 (1) ◽

pp. 121-126 ◽

Cited By ~ 10

Author(s):

V. M. Lipunov

Keyword(s):

White Dwarf ◽

Low Mass

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Discovery of a Magnetic White Dwarf/Probable Brown Dwarf Short-Period Binary

The Astrophysical Journal ◽

10.1086/491702 ◽

2005 ◽

Vol 630 (2) ◽

pp. L173-L176 ◽

Cited By ~ 24

Author(s):

Gary D. Schmidt ◽

Paula Szkody ◽

Nicole M. Silvestri ◽

Michael C. Cushing ◽

James Liebert ◽

...

Keyword(s):

White Dwarf ◽

Brown Dwarf ◽

Short Period

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Two-dimensional simulations of mixing in classical novae: The effect of white dwarf composition and mass

Astronomy and Astrophysics ◽

10.1051/0004-6361/201833422 ◽

2018 ◽

Vol 619 ◽

pp. A121 ◽

Cited By ~ 7

Author(s):

Jordi Casanova ◽

Jordi José ◽

Steven N. Shore

Keyword(s):

White Dwarf ◽

Binary Systems ◽

Main Sequence ◽

Chemical Species ◽

Two Dimensions ◽

Classical Novae ◽

Nova Shells ◽

Solar Abundances ◽

Low Mass ◽

Thermonuclear Runaway

Context. Classical novae are explosive phenomena that take place in stellar binary systems. They are powered by mass transfer from a low-mass main sequence star onto either a CO or ONe white dwarf. The material accumulates for 104–105 yr until ignition under degenerate conditions, resulting in a thermonuclear runaway. The nuclear energy released produces peak temperatures of ∼0.1–0.4 GK. During these events, 10−7−10−3 M⊙ enriched in intermediate-mass elements, with respect to solar abundances, are ejected into the interstellar medium. However, the origin of the large metallicity enhancements and the inhomogeneous distribution of chemical species observed in high-resolution spectra of ejected nova shells is not fully understood. Aims. Recent multidimensional simulations have demonstrated that Kelvin-Helmholtz instabilities that operate at the core-envelope interface can naturally produce self-enrichment of the accreted envelope with material from the underlying white dwarf at levels that agree with observations. However, such multidimensional simulations have been performed for a small number of cases and much of the parameter space remains unexplored. Methods. We investigated the dredge-up, driven by Kelvin-Helmholtz instabilities, for white dwarf masses in the range 0.8–1.25 M⊙ and different core compositions, that is, CO-rich and ONe-rich substrates. We present a set of five numerical simulations performed in two dimensions aimed at analyzing the possible impact of the white dwarf mass, and composition, on the metallicity enhancement and explosion characteristics. Results. At the time we stop the simulations, we observe greater mixing (∼30% higher when measured in the same conditions) and more energetic outbursts for ONe-rich substrates than for CO-rich substrates and more massive white dwarfs.

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