HD 98800

HD 98800, also catalogued as TV Crateris (TV Crt), is a quadruple star system in the constellation of Crater (the cup). Parallax measurements made by the Hipparcos spacecraft put it at a distance of about 150 light-years (45 parsecs) away,[7] but this value is in high error. The system is located within the TW Hydrae association (TWA), and has received the designation TWA 4.[12]

HD 98800
Observation data
Epoch J2000      Equinox J2000
Constellation Crater
HD 98800 A
Right ascension 11h 22m 05.287s[1]
Declination −24° 46′ 39.78″[1]
Apparent magnitude (V) 9.59[1]
HD 98800 B
Right ascension 11h 22m 05.288s[1]
Declination −24° 46′ 39.05″[1]
Apparent magnitude (V) 10.06[1] (10.4 / 11.5)[2]
Characteristics
HD 98800 A
Spectral type K5V / ?[3]
B−V color index 1.17 / ?[3]
HD 98800 B
Spectral type K7V / M1V[3]
B−V color index 1.37 / 1.41[3]
Variable type T Tau / RS CVn?[4][5][6]
Astrometry
Proper motion (μ) RA: -85.40[7] mas/yr
Dec.: -33.10[7] mas/yr
Parallax (π)22.27 ± 2.31[7] mas
Distanceapprox. 150 ly
(approx. 45 pc)
Absolute magnitude (MV)6.06 (Aa)[3] 6.91 ± 0.26[8] 8.02 ± 0.27[8]
Orbit[9][10]
PrimaryHD 98800 A
CompanionHD 98800 B
Period (P)246 ± 5 yr
Semi-major axis (a)1.471″
Eccentricity (e)0.5
Inclination (i)88.4 ± 2°
Longitude of the node (Ω)184.8°
Periastron epoch (T)2025
Argument of periastron (ω)
(secondary)		224.6°
Orbit[8]
PrimaryHD 98800 Ba
Period (P)314.327 ± 0.028 d
Semi-major axis (a)23.3 ± 2.5 mas
Eccentricity (e)0.7849 ± 0.0053
Inclination (i)66.8 ± 3.2°
Longitude of the node (Ω)337.6 ± 2.4°
Periastron epoch (T)MJD 52481.34 ± 0.22
Argument of periastron (ω)
(secondary)		109.6 ± 1.1°
Semi-amplitude (K1)
(primary)		22.94 ± 0.34 km/s
Semi-amplitude (K2)
(secondary)		27.53 ± 0.61 km/s
Details
Age7 ± 5[3] Myr
HD 98800 Aa
Mass1.1 ± 0.1[5] M☉
Radius1.75[11] R☉
Surface gravity (log g)4.25[11] cgs
Temperature4500[11] K
Rotational velocity (v sin i)5.0[11] km/s
HD 98800 Ba
Mass0.699 ± 0.064[8] M☉
Radius1.09 ± 0.14[8] R☉
Luminosity0.330 ± 0.075[8] L☉
Surface gravity (log g)4.21 ± 0.12[8] cgs
Temperature4200 ± 150[8] K
Rotational velocity (v sin i)3.0[11] km/s
HD 98800 Bb
Mass0.582 ± 0.051[8] M☉
Radius0.85 ± 0.11[8] R☉
Luminosity0.167 ± 0.038[8] L☉
Surface gravity (log g)4.34 ± 0.12[8] cgs
Temperature4000 ± 150[8] K
Rotational velocity (v sin i)0.0[11] km/s
Other designations
TV Crt, CD−24° 9706, GJ 2084, HD 98800, HIP 55505, SAO 179815, ADS 8141 AB, CCDM J11221-2447AB
Database references
SIMBADHD 98800
HD 98800A
HD 98800B
ARICNSHD 98800A
HD 98800B

The system consists of HD 98800 A and HD 98800 B each of which contains two stars. In 2007, a debris disk was discovered orbiting HD 98800 B consisting of two rings which indicates there may be an extrasolar planet orbiting within a distance of 1.5 to 2 astronomical units.

Stellar system

The system is a member of the TW Hydrae association, a group of young stars. Its membership was derived from the fact that its proper motion is similar to other stars in the group.[12] The system itself is estimated to be around 7-10 million years old.[13]

HD 98800 is a quadruple system, with two pairs of stars orbiting each other. The two pairs are separated by over an arcsecond,[10] so the wide visual orbit is poorly known. A preliminary range of orbits has been calculated, with an orbital period of 300 to 430 years, as well as a moderate eccentricity of 0.3 to 0.6.[10]

The primary component, HD 98800 A, is a K-type main-sequence star[3] with a varying radial velocity. This indicates the presence of another star orbiting it, but light from that star cannot be detected, so the system is a single-lined spectroscopic binary. The secondary system, HD 98800 B, is another spectroscopic binary, but double-lined since both stars (another K-type star and a red dwarf) can be directly detected. The stars in the HD 98800 are much larger than would be expected from their masses: at such a young age, these stars have not condensed into their normal size yet.[14]

Variability

The brightness of HD 98800 varies slightly between magnitudes 8.91 and 8.98, and it has been given the variable star designation TV Crateris.[4] The designation TV Crateris includes all four stars and it appears that both components A and B are variable. Component A varies with a period of 2.521 days which is thought to be its rotation period and it is classified as an RS Canum Venaticorum variable, a dwarf star with an uneven surface brightness that changes brightness as it rotates. Component B is thought to be a T Tauri star, a pre-main-sequence star surrounded by a disk.[15] It has been speculated that it is actually a post-T Tauri star and that the variations are caused by irregularities in the tilted disk intercepting the light from the star.[5]

Planetary system

Debris disk
An image of the debris disk around HD 98800 B by ALMA. The disk is misaligned with the orbital plane of the inner binary.

An infrared excess indicative of a debris disk was first discovered by IRAS.[16] Further observations of the system have been made using Keck[17] and the Spitzer Space Telescope.[18] The disk consists of two separate belts. The inner ring extends from a distance of 1.5 to 2 astronomical units from the barycenter of the central binary. The outer ring begins at approximately 5.9 astronomical units from the central binary, and extends out an undetermined distance. The gap between the two rings is ~3 astronomical units. The inner ring is thin, while the inner portion of the outer ring is dense.

Dr. Elise Furlan, leader of the Spitzer team that imaged this disk, concludes that the dust generated from the collision of rocky objects in the outer belt should eventually migrate toward the inner disk. But because the system is a double binary system, the dust particles do not evenly fill out the inner disk as expected.

The disk was imaged with ALMA and the high resolution image showed that the disk is likely misaligned with the orbit of the inner binary. The long period of the orbiting inner binary could be responsible for this misalignment and any circumbinary planet forming in this disk would be misaligned with the orbit of the inner binary.[19][9] Based on VLA observations the disk extends from 3 to 5 astronomical units. The disk is more similar to a massive gas-rich protoplanetary disks than to a debris disks, which is unusual for this kind of age of a circumbinary disk.[20]

Possible planets

Debris disks are thought to constitute a phase in planetary formation. Because of the gap within the debris disk, the possibility of a planet within the system becomes even more likely. The detected gap could be caused by a unique gravitational relationship between the disk and a possible planet already begun to form, carving out a clear space in the disk. However, the gap could also be gravitational resonance effects of the four stars.

  • An older artist's impression of the debris disk around HD 98800 B. HD 98800 A is seen in the distance. This impression was created before it was known that the disk is misaligned.

See also

References
  1. Fabricius, C.; Høg, E.; Makarov, V. V.; Mason, B. D.; Wycoff, G. L.; Urban, S. E. (2002). "The Tycho double star catalogue". Astronomy and Astrophysics. 384: 180–189. Bibcode:2002A&A...384..180F. doi:10.1051/0004-6361:20011822.
  2. "Sixth Catalog of Orbits of Visual Binary Stars". United States Naval Observatory.
  3. Song, Inseok; Caillault, J.-P.; Barrado y Navascués, David; Stauffer, John R.; Randich, Sofia (April 2000), "Ages of Late Spectral Type Vega-like Stars", The Astrophysical Journal, 533 (1): L41–L44, arXiv:astro-ph/0002323, Bibcode:2000ApJ...533L..41S, doi:10.1086/312597, PMID 10727387, S2CID 41394330
  4. Samus, N. N.; Durlevich, O. V.; et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)". VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S. 1: B/gcvs. Bibcode:2009yCat....102025S.
  5. Verrier, P. E.; Evans, N. W. (2008). "HD 98800: A most unusual debris disc". Monthly Notices of the Royal Astronomical Society. 390 (4): 1377. arXiv:0807.5105. Bibcode:2008MNRAS.390.1377V. doi:10.1111/j.1365-2966.2008.13854.x. S2CID 119182238.
  6. "TV Crt". International Variable Star Index. Retrieved 2020-07-09.
  7. van Leeuwen, F.; et al. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653–664. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357. S2CID 18759600.
  8. Boden, Andrew F.; Sargent, Anneila I.; Akeson, Rachel L.; Carpenter, John M.; Torres, Guillermo; Latham, David W.; Soderblom, David R.; Nelan, Ed; Franz, Otto G.; Wasserman, Lawrence H. (2005). "Dynamical Masses for Low‐Mass Pre–Main‐Sequence Stars: A Preliminary Physical Orbit for HD 98800 B". The Astrophysical Journal. 635 (1): 442–451. arXiv:astro-ph/0508331. Bibcode:2005ApJ...635..442B. doi:10.1086/497328. S2CID 15698880.
  9. Kennedy, Grant M.; Matrà, Luca; Facchini, Stefano; Milli, Julien; Panić, Olja; Price, Daniel; Wilner, David J.; Wyatt, Mark C.; Yelverton, Ben M. (February 2019). "Publisher Correction: A circumbinary protoplanetary disk in a polar configuration". NatAs. 3 (3): 278. arXiv:1901.05018. Bibcode:2019NatAs...3..278K. doi:10.1038/s41550-019-0715-1. ISSN 2397-3366.
  10. Tokovinin, A. A. (1999). "The visual orbit of HD 98800". Astronomy Letters. 25 (10): 669–671. Bibcode:1999AstL...25..669T.
  11. Laskar, Tanmoy; Soderblom, David R.; Valenti, Jeff A.; Stauffer, John R. (2009). "The Metallicity of the Hd 98800 System". The Astrophysical Journal. 698 (1): 660–665. arXiv:0905.1907. Bibcode:2009ApJ...698..660L. doi:10.1088/0004-637X/698/1/660. S2CID 15230160.
  12. Gagné, Jonathan; Faherty, Jacqueline K.; Mamajek, Eric E.; Malo, Lison; Doyon, René; Filippazzo, Joseph C.; Weinberger, Alycia J.; Donaldson, Jessica K.; Lépine, Sébastien; Lafrenière, David; Artigau, Étienne; Burgasser, Adam J.; Looper, Dagny; Boucher, Anne; Beletsky, Yuri; Camnasio, Sara; Brunette, Charles; Arboit, Geneviève (2017). "BANYAN. IX. The Initial Mass Function and Planetary-mass Object Space Density of the TW HYA Association". The Astrophysical Journal Supplement Series. 228 (2): 18. arXiv:1612.02881. Bibcode:2017ApJS..228...18G. doi:10.3847/1538-4365/228/2/18. S2CID 118920136.
  13. Ribas, Álvaro; Macías, Enrique; Espaillat, Catherine C.; Duchêne, Gaspard (2018). "Long-lived Protoplanetary Disks in Multiple Systems: The VLA View of HD 98800". The Astrophysical Journal. 865 (1): 77. arXiv:1808.02493. Bibcode:2018ApJ...865...77R. doi:10.3847/1538-4357/aad81b. S2CID 118912551.
  14. "Encyclopedia of Science: T Tauri star". Retrieved 17 January 2017.
  15. Messina, S.; Desiderata, S.; Taratto, M.; Lanzafame, A. C.; Guinan, E. F. (September 2010). "RACE-OC project: Rotation and variability of young stellar associations within 100 pc". Astronomy and Astrophysics. 520: 63. arXiv:1004.1959. Bibcode:2010A&A...520A..15M. doi:10.1051/0004-6361/200913644. S2CID 118569400.
  16. Walker and Wolstencroft (1988). "Cool circumstellar matter around nearby main-sequence stars". Publications of the Astronomical Society of the Pacific. 100: 1509–1521. Bibcode:1988PASP..100.1509W. doi:10.1086/132357.
  17. Koerner; Jensen, E. L. N.; Cruz, K. L.; Guild, T. B.; Gultekin, K. (2000). "A Single Circumbinary Disk in the HD 98800 Quadruple System". The Astrophysical Journal. 533 (1): L37–L40. arXiv:astro-ph/0002227. Bibcode:2000ApJ...533L..37K. doi:10.1086/312593. PMID 10727386. S2CID 17714246.
  18. Furlan, E.; et al. (2007). "HD 98800: A 10 Myr Old Transition Disk". The Astrophysical Journal. 664 (2): 1176–1184. arXiv:0705.0380. Bibcode:2007ApJ...664.1176F. doi:10.1086/519301. S2CID 14027663.
  19. Czekala, Ian; Chiang, Eugene; Andrews, Sean M.; Jensen, Eric L. N.; Torres, Guillermo; Wilner, David J.; Stassun, Keivan G.; Macintosh, Bruce (September 2019). "The Degree of Alignment between Circumbinary Disks and Their Binary Hosts". Astrophysical Journal. 883 (1): 22. arXiv:1906.03269. Bibcode:2019ApJ...883...22C. doi:10.3847/1538-4357/ab287b. ISSN 0004-637X. S2CID 182952526.
  20. Ribas, Álvaro; Macías, Enrique; Espaillat, Catherine C.; Duchêne, Gaspard (September 2018). "Long-lived Protoplanetary Disks in Multiple Systems: The VLA View of HD 98800". Astrophysical Journal. 865 (1): 77. arXiv:1808.02493. Bibcode:2018ApJ...865...77R. doi:10.3847/1538-4357/aad81b. ISSN 0004-637X.
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