38 Geminorum
Quadruple star system in the constellation Gemini
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38 Geminorum is a quadruple star system in the northern zodiac constellation of Gemini. It has the Bayer designation e Geminorum, while 38 Geminorum is the Flamsteed designation. This system is visible to the naked eye as a faint, white-hued point of light with an apparent visual magnitude of 4.71. The system is located about 98 light years away from the Sun based on parallax, and is drifting further away with a radial velocity of +16 km/s.[19] It is a potential member of the Tucana–Horologium stellar kinematic group.[20]
 | |
| Observation data Epoch J2000 Equinox ICRS | |
|---|---|
| Constellation | Gemini |
| A | |
| Right ascension | 06h 54m 38.63815s[1] |
| Declination | +13° 10′ 40.2431″[1] |
| Apparent magnitude (V) | 4.75[2] |
| B | |
| Right ascension | 06h 54m 38.92062s[3] |
| Declination | +13° 10′ 34.1871″[3] |
| Apparent magnitude (V) | 7.80[2] |
| UPM J0654+1310 | |
| Right ascension | 06h 54m 48.77255s[4] |
| Declination | +13° 10′ 03.4482″[4] |
| Apparent magnitude (V) | 15.1[5] |
| Characteristics | |
| A | |
| Evolutionary stage | main sequence (Aa)[6] |
| Spectral type | F0V + F7/8V[7] |
| U−B color index | +0.07[8] |
| B−V color index | +0.30[8] |
| Variable type | Suspected δ Sct[9] |
| B | |
| Evolutionary stage | main sequence[10] |
| Spectral type | G6V[11] |
| UPM J0654+1310 | |
| Evolutionary stage | main sequence[10] |
| Spectral type | dMp3.5[12] |
| Astrometry | |
| A | |
| Radial velocity (Rv) | +30.46±0.09 km/s |
| Proper motion (μ) | RA: +68.745[1] mas/yr Dec.: −86.832[1] mas/yr |
| Parallax (π) | 33.9184±0.8248 mas[1] |
| Distance | 96 ± 2 ly (29.5 ± 0.7 pc) |
| Absolute magnitude (MV) | +2.50[13] |
| B | |
| Radial velocity (Rv) | +22.6±2[14] km/s |
| Proper motion (μ) | RA: +89.385[3] mas/yr Dec.: −76.967[3] mas/yr |
| Parallax (π) | 33.3248±0.0384 mas[3] |
| Distance | 97.9 ± 0.1 ly (30.01 ± 0.03 pc) |
| UPM J0654+1310 | |
| Radial velocity (Rv) | +25.59±3.25[4] km/s |
| Proper motion (μ) | RA: +71.706[4] mas/yr Dec.: −85.515[4] mas/yr |
| Parallax (π) | 33.2912±0.0248 mas[4] |
| Distance | 97.97 ± 0.07 ly (30.04 ± 0.02 pc) |
| Orbit[15] | |
| Primary | 38 Gem Aa |
| Name | 38 Gem Ab |
| Period (P) | 174.7±0.1 days |
| Semi-major axis (a) | 0.85–0.90 au[a] |
| Eccentricity (e) | 0.24±0.02 |
| Inclination (i) | 48–52° |
| Periastron epoch (T) | 59418.3±0.1 HJD |
| Argument of periastron (ω) (secondary) | 258±3° |
| Semi-amplitude (K1) (primary) | 17.3±0.5 km/s |
| Semi-amplitude (K2) (secondary) | 25.4±0.5 km/s |
| Details | |
| 38 Gem Aa | |
| Mass | 1.61+0.06 −0.05[15] M☉ |
| Radius | 1.97[7] R☉ |
| Luminosity | 7.9+1.0 −0.8[15] L☉ |
| Surface gravity (log g) | 4.0±0.5[15] cgs |
| Temperature | 7,500±250[15] K |
| Metallicity [Fe/H] | −0.08±0.06[16] dex |
| Rotational velocity (v sin i) | 150±20[15] km/s |
| Age | 993+220 −190[15] Myr |
| 38 Gem Ab | |
| Mass | 1.12+0.23 −0.10[15] M☉ |
| Radius | 1.16[7] R☉ |
| Luminosity | 1.07+1.38 −0.63[15] L☉ |
| Surface gravity (log g) | 4.0±0.5[15] cgs |
| Temperature | 6,000±250[15] K |
| Rotational velocity (v sin i) | 5±1[15] km/s |
| Age | 993+220 −190[15] Myr |
| 38 Gem B | |
| Mass | 0.89[17] M☉ |
| Radius | 0.88[18] R☉ |
| Luminosity | 0.69[18] L☉ |
| Surface gravity (log g) | 4.55[18] cgs |
| Temperature | 5,614[18] K |
| Age | 993+220 −190[15] Myr |
| UPM J0654+1310 | |
| Mass | 0.25[10] M☉ |
| Radius | 0.25[18] R☉ |
| Luminosity | 0.0062[18] L☉ |
| Surface gravity (log g) | 4.99[18] cgs |
| Temperature | 3,261[18] K |
| Age | 993+220 −190[15] Myr |
| Other designations | |
| e Gem, 38 Gem, NSV 3266, BD+13°1462, GJ 9220, HD 50635, HIP 33202, HR 2564, SAO 96265, WDS J06546+1311 | |
| Database references | |
| SIMBAD | data |
| B | |
| UPM J0654+1310 | |
Characteristics
The primary component, e Geminorum Aa, is an F-type main-sequence star[7] which has about 1.61 times the mass of the Sun,[15] 1.97 times the radius of the Sun[7] and an effective temperature of 7,500 K.[15] It is a suspected chemically peculiar star of subtype CP1 (an Am star),[22] which Slettebak (1955) classified as kA8mF0Vp.[23] This notation indicates the star displays the calcium K line of an A8 star and the metal lines of an F0V star. In 1949, J. Hopmann catalogued it as a suspected Delta Scuti variable.[9]
The primary is closely orbited by companion e Geminorum Ab, which is a smaller F-type main-sequence star[7] with 1.12 times the radius of the Sun and a temperature of 6,000 K.[15] It can explain the X-ray emission coming from the system. The system has been resolved using interferometry, which obtained an projected separation of 0.44 astronomical units (66,000,000 km). Combined with the masses, this results in an estimated orbital period of about two months.[7] An orbital solution was provided in 2026, yielding an orbital period of 174.7 days, a semi-major axis of 0.85–0.90 astronomical units (127,000,000–135,000,000 km), an inclination between 48 and 52° and a low eccentricity of 0.24.[15][a]
The Aa-Ab system is orbited by the component B, which has a projected separation of 184.3 AU.[17] Two sets of low quality orbital elements have been computed for this system, yielding periods of 1,943.8 years and 3,190 years, and eccentricities of 0.150 and 0.485, respectively.[24] As of 2018, the pair had an angular separation of 7.4″ (implying a projected separation of 220 au[7]) along a position angle of 143°.[2] Star B is a G-type main-sequence star with a class of G6V,[11] 0.95 times the Sun's mass,[17] 0.88 times the Sun's radius and an estimated effective temperature of 5,614 K.[18]
The most distant component, UPM J0654+1310, has a projected separation of 4,560 au and is believed to be a red dwarf with a mass of just 0.3 M☉.[7]