Ross 640

Ross 640 is a white dwarf star in the northern constellation of Hercules, positioned near the constellation border with Corona Borealis. With an apparent visual magnitude of 13.83,[2] it is too faint to be visible to the naked eye. Its trigonometric parallax from the Gaia mission is 62.9″,[1] corresponding to a distance of 52 light-years (15.9 parsecs).

Ross 640
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Hercules
Right ascension 16h 28m 25.00303s[1]
Declination +36° 46′ 15.8492″[1]
Apparent magnitude (V) 13.83[2]
Characteristics
Evolutionary stage white dwarf
Spectral type DZA5.5[3]
Astrometry
Proper motion (μ) RA: −494.185[1] mas/yr
Dec.: +746.554[1] mas/yr
Parallax (π)62.9147 ± 0.0223[1] mas
Distance51.84 ± 0.02 ly
(15.895 ± 0.006 pc)
Absolute magnitude (MV)+13.01[4]
Details
Mass0.58±0.03[5] M☉
Luminosity0.0007[5] L☉
Surface gravity (log g)7.76[6] cgs
Temperature8,100[7] K
Age1.02[6] Gyr
Other designations
GJ 9564, LTT 14906, WD 1626+368[8]
Database references
SIMBADdata

This compact star has a stellar classification of DZA5.5, indicating a metal-rich atmosphere accompanied by weaker lines of hydrogen.[3] A detailed analysis of its spectrum revealed that Ross 640 is a relatively cool white dwarf with an effective temperature of approximately 8,100 K, which means that it has been in the white dwarf phase for slightly more than 1 billion years.[7] Ross 640 has a spectrum characterized by hydrogen Balmer lines in the visible and very strong ionized magnesium lines in the ultraviolet.[9] The presence of heavy elements in the photosphere of Ross 640 indicates that it recently accreted rocky debris from its planetary system.

References
  1. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  2. Bergeron, P.; Leggett, S. K.; Ruiz, María Teresa (2001). "Photometric and Spectroscopic Analysis of Cool White Dwarfs with Trigonometric Parallax Measurements". The Astrophysical Journal Supplement Series. 133 (2): 413–450. arXiv:astro-ph/0011286. Bibcode:2001ApJS..133..413B. doi:10.1086/320356. ISSN 0067-0049.
  3. Wesemael, F.; et al. (1993). "An atlas of optical spectra of white-dwarf stars". Publications of the Astronomical Society of the Pacific. 105: 761. Bibcode:1993PASP..105..761W. doi:10.1086/133228.
  4. Limoges, M. -M; Bergeron, P.; Lépine, S. (2015). "Physical Properties of the Current Census of Northern White Dwarfs within 40 pc of the Sun". The Astrophysical Journal Supplement Series. 219 (2): 19. arXiv:1505.02297. Bibcode:2015ApJS..219...19L. doi:10.1088/0067-0049/219/2/19.
  5. Toonen, S.; Hollands, M.; Gänsicke, B. T.; Boekholt, T. (2017). "The binarity of the local white dwarf population". Astronomy and Astrophysics. 602: A16. arXiv:1703.06893. Bibcode:2017A&A...602A..16T. doi:10.1051/0004-6361/201629978.
  6. Holberg, J. B.; Oswalt, T. D.; Sion, E. M.; McCook, G. P. (2016). "The 25 parsec local white dwarf population". Monthly Notices of the Royal Astronomical Society. 462 (3): 2295. Bibcode:2016MNRAS.462.2295H. doi:10.1093/mnras/stw1357. hdl:10150/621732.
  7. Blouin, S.; Dufour, P.; Allard, N. F. (23 August 2018). "A New Generation of Cool White Dwarf Atmosphere Models. I. Theoretical Framework and Applications to DZ Stars". The Astrophysical Journal. 863 (2): 184. arXiv:1807.06616. Bibcode:2018ApJ...863..184B. doi:10.3847/1538-4357/aad4a9.
  8. "ross 640". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2019-08-20.
  9. Zeidler-K.T., E.-M.; Weidemann, V.; Koester, D. (1986). "Metal abundances in helium-rich white dwarf atmospheres". Astronomy & Astrophysics. 155 (2): 356–370. Bibcode:1986A&A...155..356Z.
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