SDSS 1557 (SDSS J155720.77+091624.6, WD 1554+094) is a binary system composed of a white dwarf and a brown dwarf. The system is surrounded by a circumbinary debris disk. The debris disk was formed when a minor planet was tidally disrupted around the white dwarf in the past.[1][3]
.jpg) Artist's impression of the SDSS1557 system. The white dwarf is the blue star that accretes material from a stream. Right next to it is the brown dwarf and around the binary is the debris disk. Credit: International Gemini Observatory/NOIRLab/NSF/AURA/UCL/University of Warwick/University of Sheffield//Mark Garlick | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Serpens |
| Right ascension | 15h 57m 20.77s |
| Declination | +09° 16′ 24.6″ |
| Characteristics | |
| Evolutionary stage | post common envelope binary: white dwarf + brown dwarf |
| Spectral type | DAZ + L4±1[1] |
| Astrometry | |
| Proper motion (μ) | RA: -10.202 ±0.198 mas/yr[2] Dec.: -25.988 ±0.197 mas/yr[2] |
| Parallax (π) | 1.7767 ± 0.1974 mas[2] |
| Distance | approx. 1631 ly (500.0+19.8 −18.0 pc)[3] |
| Orbit[1] | |
| Primary | SDSS 1557A |
| Companion | SDSS 1557B |
| Period (P) | 2.273153 ±0.000002 hrs |
| Semi-major axis (a) | 0.70 ± 0.02 R☉ |
| Inclination (i) | 80 ±3[3]° |
| Semi-amplitude (K1) (primary) | 40.42 ±0.69 km/s |
| Semi-amplitude (K2) (secondary) | 288.3 ±3.0 km/s |
| Details[1][3] | |
| SDSS 1557A | |
| Mass | 0.447 ±0.043 M☉ |
| Radius | 0.0162 ±0.0012 R☉ |
| Surface gravity (log g) | 7.63 ±0.11 cgs |
| Temperature | 21800 ±800 K |
| Age | 33 ±5 (cooling age) Myr |
| SDSS 1557B | |
| Mass | 66+5 −7 MJup |
| Radius | 1.054 ±0.242 RJup |
| Temperature | 1400 to 2500 K |
| Other designations | |
GALEX J155720.8+091625, WD 1554+094, SDSS J155720.78+091624.7, ULAS J155720.77+091624.6, EQ J1557+0916 | |
| Database references | |
| SIMBAD | data |
The brown dwarf companion
editIn 2011 it was found that the system did show Y- and J-band excess, which hinted at a companion.[4] Follow-up observations with instruments on the Gemini Observatory and the Very Large Telescope revealed the secondary, the brown dwarf SDSS 1557B, and a circumbinary disk around the binary. The researchers measured the radial velocity changes with the help of the Magnesium absorption line at 4482 Å and found that a 66 MJ brown dwarf orbits the white dwarf at around 0.7 R☉, with the orbital period being around 2.27 hours. The irradiated brown dwarf also shows a hydrogen-alpha emission line.[1]
Additional follow-up came with Hubble WFC3, using time-resolved spectrophotometry. SDSS 1557B is similar to ultra-short period planets and is likely tidally locked. White dwarfs give off more radiation in the ultra-violet than it is the case for main-sequence stars. This leads to a higher UV-exposure for SDSS 1557B when compared to a regular hot Jupiter. The fact that SDSS 1557B is tidally locked creates vast temperature changes in the dayside and nightside of the brown dwarf. The researchers found that the brown dwarf is inefficient at redistributing the heat from the dayside to the nightside. They also find that the nightside is likely dominated by clouds and the dayside is likely dominated by opaque H− and likely has a temperature inversion.[3]
The circumbinary disk
editThe system was first suspected to be a white dwarf with a circumstellar disk in 2011 from K-band excess.[4] The system also displayed high metal abundances (Ca, Mg, Si), showing that the white dwarf was polluted with planetary debris.[5][1]
The disk ring lies at around 3.3 R☉, exterior to the Roche lobe. The dust grains of the disk have a temperature of 1,100 Kelvin (K). The material from the disk crosses the gap between disk and white dwarf in streams.[1] A process that is well known for binaries[6] and seen in other binaries, such as CoRoT 223992193.[7]
Past evolution of the system
editThe system formed at least 1.5 Gyr ago as a low-mass-ratio binary of a star (1.06–1.85 M☉) and a companion with a semi-major axis of less than one astronomical unit (AU) in the past.[1][8] The minor planet on the other hand had an orbit that was larger than a few AU. The brown dwarf was engulfed when the star became a giant, an evolutionary stage known as common envelope. Around 33 Myrs ago the common envelope was ejected, forming a low-mass Helium core white dwarf. This formed the present binary, called SDSS 1557. A minor planet, likely an asteroid larger than 4 km, with a mass of at least 1014 kg survived the giant phase of the star. It was scattered towards the binary and tidally disrupted by the white dwarf when it crossed the Roche radius. The resulting debris cloud became the disk we see today.[1]
See also
edit- List of exoplanets and planetary debris around white dwarfs
- Post common envelope binary
- WD 0137−349 another white dwarf-brown dwarf binary
References
edit- ^ a b c d e f g h i Farihi, J.; Parsons, S. G.; Gänsicke, B. T. (2017-03-01). "A circumbinary debris disk in a polluted white dwarf system". Nature Astronomy. 1 (3): 0032. arXiv:1612.05259. Bibcode:2017NatAs...1E..32F. doi:10.1038/s41550-016-0032. ISSN 2397-3366.
- ^ a b Brown, A. G. A.; et al. (Gaia collaboration) (2021). "Gaia Early Data Release 3: Summary of the contents and survey properties". Astronomy & Astrophysics. 649: A1. arXiv:2012.01533. Bibcode:2021A&A...649A...1G. doi:10.1051/0004-6361/202039657. S2CID 227254300. (Erratum: doi:10.1051/0004-6361/202039657e). Gaia EDR3 record for this source at VizieR.
- ^ a b c d e Amaro, Rachael C.; Apai, Dániel; Lew, Ben W. P.; Zhou, Yifan; Lothringer, Joshua D.; Casewell, Sarah L.; Tan, Xianyu; Barman, Travis; Marley, Mark S.; Mayorga, L. C.; Parmentier, Vivien (2024-05-01). "Time-resolved Hubble Space Telescope Wide Field Camera 3 Spectrophotometry Reveals Inefficient Day-to-night Heat Redistribution in the Highly Irradiated Brown Dwarf SDSS 1557B". The Astrophysical Journal. 966 (1): 4. arXiv:2404.08087. Bibcode:2024ApJ...966....4A. doi:10.3847/1538-4357/ad354c. ISSN 0004-637X.
- ^ a b Steele, P. R.; Burleigh, M. R.; Dobbie, P. D.; Jameson, R. F.; Barstow, M. A.; Satterthwaite, R. P. (2011-10-01). "White dwarfs in the UKIRT Infrared Deep Sky Survey Large Area Survey: the substellar companion fraction". Monthly Notices of the Royal Astronomical Society. 416 (4): 2768–2791. arXiv:1106.5893. Bibcode:2011MNRAS.416.2768S. doi:10.1111/j.1365-2966.2011.19225.x. ISSN 0035-8711.
- ^ Farihi, J.; Gänsicke, B. T.; Steele, P. R.; Girven, J.; Burleigh, M. R.; Breedt, E.; Koester, D. (2012-04-01). "A trio of metal-rich dust and gas discs found orbiting candidate white dwarfs with K-band excess". Monthly Notices of the Royal Astronomical Society. 421 (2): 1635–1643. arXiv:1112.5163. Bibcode:2012MNRAS.421.1635F. doi:10.1111/j.1365-2966.2012.20421.x. ISSN 0035-8711.
- ^ Artymowicz, Pawel; Lubow, Stephen H. (1996-08-01). "Mass Flow through Gaps in Circumbinary Disks". The Astrophysical Journal. 467 (2): L77–L80. Bibcode:1996ApJ...467L..77A. doi:10.1086/310200. ISSN 0004-637X.
- ^ Terquem, Caroline; Sørensen-Clark, Paul Magnus; Bouvier, Jérôme (2015-12-01). "A circumbinary disc model for the variability of the eclipsing binary CoRoT 223992193". Monthly Notices of the Royal Astronomical Society. 454 (4): 3472–3479. arXiv:1509.08509. Bibcode:2015MNRAS.454.3472T. doi:10.1093/mnras/stv2258. ISSN 0035-8711.
- ^ Zorotovic, Monica; Schreiber, MatthiasR (2022-07-01). "Close detached white dwarf + brown dwarf binaries: further evidence for low values of the common envelope efficiency". Monthly Notices of the Royal Astronomical Society. 513 (3): 3587–3595. arXiv:2204.13715. Bibcode:2022MNRAS.513.3587Z. doi:10.1093/mnras/stac1137. ISSN 0035-8711.