Struve 2398

Struve 2398 (Gliese 725) is a binary star system in the northern constellation of Draco. Struve 2398 is star number 2398 in the Struve Double Star Catalog of Baltic-German astronomer Friedrich Georg Wilhelm von Struve. The astronomer's surname, and hence the star identifier, is sometimes indicated by a Greek sigma, Σ. Although the components are too faint to be viewed with the naked eye, this star system is among the closest to the Sun. Parallax measurements by the Hipparcos spacecraft give them an estimated distance of about 11.6 light years away.[1]

Struve 2398 AB
Observation data
Epoch J2000      Equinox J2000
Constellation Draco
Struve 2398 A
Right ascension 18h 42m 46.67934s[1]
Declination +59° 37′ 49.4724″[1]
Apparent magnitude (V) 8.94[2]
Struve 2398 B
Right ascension 18h 42m 46.96652s[1]
Declination +59° 37′ 36.3471″[1]
Apparent magnitude (V) 9.70
Characteristics
Spectral type M3 V + M3.5 V[3]
U−B color index 1.11/1.14
B−V color index 1.53/1.59
Variable type Flare star
Astrometry
Struve 2398 A
Radial velocity (Rv)–1.07[4] km/s
Proper motion (μ) RA: –1311.33[1] mas/yr
Dec.: +1795.08[1] mas/yr
Parallax (π)283.54 ± 0.41[5] mas
Distance11.50 ± 0.02 ly
(3.527 ± 0.005 pc)
Struve 2398 B
Radial velocity (Rv)1.09[4] km/s
Proper motion (μ) RA: –1400.75[1] mas/yr
Dec.: +1858.53[1] mas/yr
Parallax (π)286.39 ± 0.83[5] mas
Distance11.39 ± 0.03 ly
(3.49 ± 0.01 pc)
Details
Struve 2398 A
Mass0.334±0.033[3] M☉
Radius0.351±0.013[3] R☉
Luminosity0.039 L☉
Temperature3,441±60[3] K
Metallicity [Fe/H]−0.23±0.08[3] dex
Rotational velocity (v sin i)< 2.5[6] km/s
Age3.0[3] Gyr
Struve 2398 B
Mass0.248±0.025[3] M☉
Radius0.273±0.011[3] R☉
Luminosity0.021 L☉
Temperature3,345±60[3] K
Metallicity [Fe/H]−0.30±0.08[3] dex
Rotational velocity (v sin i)< 2.5[6] km/s
Age2.4[3] Gyr
Orbit[7]
CompanionStruve 2398 B
Period (P)294.7 yr
Semi-major axis (a)10.50″
Eccentricity (e)0.70
Inclination (i)52.5°
Longitude of the node (Ω)139.9°
Periastron epoch (T)1778.0
Argument of periastron (ω)
(secondary)		203.8°
Other designations
ADS 11632, BD +59°1915, GCTP 4330.00 A/B, Gl 725 A/B.
Struve 2398 A: G 227-046, HD 173739, HIP 91768, LHS 58, Vyssotsky 184.
Struve 2398 B: G 227-047, HD 173740, HIP 91772, LHS 91772.
Database references
SIMBADThe system
A
B

Both stars are small red dwarfs, with each having around a third the Sun's mass and radius. They each display the type of variability common to flare stars,[8] and their active surfaces are sources of X-ray emission.[9] The orbital period for the pair is about 295 years, with an average distance of about 56 astronomical units,[10] and the eccentricity of their orbit is 0.70.

The pair has a relatively high proper motion of 2.2 arc seconds per year. The system is on an orbit through the Milky Way that has an eccentricity of 0.05, carrying them as close as 8 kpc and as far as 9 kpc from the Galactic Center. The plane of their galactic orbit carries them as far as 463−489 pc away from the galactic plane.[11]

Planetary system

In 2019 two candidate planets were detected in orbit around component B using the radial velocity method.[12]

The Struve 2398 B (Gliese 725 B) planetary system
Companion
(in order from star)		 Mass Semimajor axis
(AU)		 Orbital period
(days)		 Eccentricity Inclination Radius
b 15.7±5.7 M⊕ 0.261+0.022
−0.028		 91.29+0.31
−0.24		 0.06+0.26
−0.06		 — —
c 13.1+8.1
−6.4 M⊕		 0.428+0.037
−0.045		 192.4+2.2
−1.9		 0.03+0.22
−0.03		 — —

See also
  • List of nearest stars

References
  1. van Leeuwen, F. (November 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.
  2. Rojas-Ayala, Bárbara; et al. (April 2012). "Metallicity and Temperature Indicators in M Dwarf K-band Spectra: Testing New and Updated Calibrations with Observations of 133 Solar Neighborhood M Dwarfs". The Astrophysical Journal. 748 (2): 93. arXiv:1112.4567. Bibcode:2012ApJ...748...93R. doi:10.1088/0004-637X/748/2/93. S2CID 41902340. See Table 3.
  3. Mann, Andrew W.; et al. (May 2015), "How to Constrain Your M Dwarf: Measuring Effective Temperature, Bolometric Luminosity, Mass, and Radius", The Astrophysical Journal, 804 (1): 38, arXiv:1501.01635, Bibcode:2015ApJ...804...64M, doi:10.1088/0004-637X/804/1/64, S2CID 19269312, 64.
  4. Nidever, David L.; et al. (August 2002). "Radial Velocities for 889 Late-Type Stars". The Astrophysical Journal Supplement Series. 141 (2): 503–522. arXiv:astro-ph/0112477. Bibcode:2002ApJS..141..503N. doi:10.1086/340570. S2CID 51814894.
  5. Martell, Sarah; et al. (2016). "The GALAH Survey: Observational Overview and Gaia DR1 companion". Monthly Notices of the Royal Astronomical Society. 465 (3): 3203–3219. arXiv:1609.02822. Bibcode:2017MNRAS.465.3203M. doi:10.1093/mnras/stw2835. S2CID 59406091.
  6. Reiners, Ansgar; et al. (April 2012), "A Catalog of Rotation and Activity in Early-M Stars", The Astronomical Journal, 143 (4): 15, arXiv:1201.5774, Bibcode:2012AJ....143...93R, doi:10.1088/0004-6256/143/4/93, S2CID 118425326, 93.
  7. Baize, P. (October 1976). "Orbital elements of eighteen visual double stars". Astronomy and Astrophysics Supplement Series. 26: 177–193. Bibcode:1976A&AS...26..177B. Listed as ADS 11632.
  8. Pettersen, B. R. (1991), "The nearby flare stars", Società Astronomica Italiana, Memorie, 62: 217–242, Bibcode:1991MmSAI..62..217P.
  9. Schmitt, J. H. M. M.; Fleming, T. A.; Giampapa, M. S. (September 1995). "The X-ray view of the low-mass stars in the solar neighborhood". The Astrophysical Journal. 450 (9): 392–400. Bibcode:1995ApJ...450..392S. doi:10.1086/176149.
  10. "Struve 2398 AB". Retrieved 2010-10-22.
  11. Allen, C.; Herrera, M. A. (1998), "The galactic orbits of nearby UV Ceti stars", Revista Mexicana de Astronomía y Astrofísica, 34: 37–46, Bibcode:1998RMxAA..34...37A.
  12. Barnes, J. R.; et al. (2019-06-11), Frequency of planets orbiting M dwarfs in the Solar neighbourhood, arXiv:1906.04644v1
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