36 Serpentis

This article is about b Serpentis and is not to be confused with β (Beta) Serpentis.

36 Serpentis is a triple star^[9] system in the equatorial constellation of Serpens. It has the Bayer designation b Serpentis, while 36 Serpentis is the Flamsteed designation.^[12] The system is visible to the naked eye as a dim, white-hued point of light with a combined apparent visual magnitude of 5.09.^[2] It is located 162 light years away from the Sun based on parallax,^[1] and is moving closer with a radial velocity of −8 km/s.^[8]

36 Serpentis

Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Serpens
Right ascension	15h 51m 15.59418s[1]
Declination	−03° 05′ 25.7938″[1]
Apparent magnitude (V)	5.09[2] (5.2 + 7.8)[3]
Characteristics
Spectral type	A3Vn[4] or A2IV-Vn[5] (A7 + G0)[6]
U−B color index	+0.07[7]
B−V color index	+0.12[7]
Astrometry
Radial velocity (Rv)	−8[8] km/s
Proper motion (μ)	RA: −91.09[1] mas/yr Dec.: −28.21[1] mas/yr
Parallax (π)	20.10±0.33 mas[1]
Distance	162 ± 3 ly (49.8 ± 0.8 pc)
Absolute magnitude (MV)	1.61[2]
Orbit[9]
Primary	36 Ser A
Companion	36 Ser B
Period (P)	1,073 days
Eccentricity (e)	0.7
Semi-amplitude (K1) (primary)	6 km/s
Orbit[6]
Primary	36 Ser AB
Companion	36 Ser C
Period (P)	50.6±1.5 yr
Semi-major axis (a)	0.400±0.006″
Eccentricity (e)	0.8323±0.0047
Inclination (i)	98.08±0.31°
Longitude of the node (Ω)	74.00±0.31°
Periastron epoch (T)	2002.78±0.17
Argument of periastron (ω) (secondary)	72.84±0.91°
Details
36 Ser A
Mass	1.97[9] M☉
Radius	2.25[9] R☉
Luminosity	19.13[2] L☉
Surface gravity (log g)	3.89[10] cgs
Temperature	8,213[9] K
Metallicity [Fe/H]	−2.00[10] dex
Rotational velocity (v sin i)	229[11] km/s
Age	710[9] Myr
36 Ser B
Mass	≥0.37 and ≤0.50[9] M☉
36 Ser C
Mass	1.27[9] M☉
Radius	1.26[9] R☉
Temperature	6,255[9] K
Age	710[9] Myr
Other designations
b Ser, 36 Ser, BD−02°4058, FK5 2249, GC 4210, HD 141851, HIP 77660, HR 5895, SAO 140801, WDS J15513-0305[12]
Database references
SIMBAD	data

Characteristics

The system consists of two spectroscopic binaries. The inner pair contains components A and B, while the outer pair contains components AB and C. The age of the whole system is estimated at 710 million years.^[9]

The components AB and C orbit each other over a long orbital period of 52.8 years and a high eccentricity of 0.83.^[6] Gray et al. (2017) found a merged stellar classification of A2IV-Vn for this system,^[5] while Cowley et al. matched it with a class of A3Vn,^[4] where the 'n' indicates "nebulous" lines caused by rapid rotation.

The primary component, 36 Serpentis A, is an A7-class^[6] main sequence star of visual magnitude 5.2.^[3] It is spinning rapidly, showing a projected rotational velocity of 229 km/s.^[11] It was once thought to be a Lambda Boötis star^[13] but this is now disputed.^[9] The star is 710 million years old with 1.97 times the mass of the Sun and 2.25 times the Sun's radius.^[9] It is radiating 19 times the Sun's luminosity from its photosphere^[2] at an effective temperature of 8,213 K.^[9]

The secondary, 36 Serpentis B, has been detected only by spectroscopy. It has an orbital period of 1,073 days (2.94 years) and a high eccentricity of 0.7. Interferometric observations have failed to detect this star, implying a luminosity-derived mass less than 0.50 M_☉. The radial velocity data suggest a mass of at least 0.37 solar masses. It may be a faint red dwarf or a white dwarf. 36 Ser B is likely the source for the X-ray emission that has been detected coming from this system.^[9]

The tertiary, 36 Serpentis C, is a G0 star^[6] with a visual magnitude of 7.8.^[3] It has 1.27 times the Sun's mass, 1.26 times the Sun's radius, and an effective temperature of 6,555 K.^[9]