1 Delphini (1 Del) is the Flamsteed designation for a close binary star in the equatorial constellation Delphinus. With a combined apparent magnitude of 6.08, it is barely visible to the naked eye, even under ideal conditions. Parallax measurements put the components at a distance 703 and 780 light years respectively. However, its approaching the Solar System with a radial velocity of 15 km/s.

1 Delphini

Location of 1 Delphini (circled)
Observation data Epoch J2000      Equinox J2000
Constellation	Delphinus
A
Right ascension	20h 30m 17.9623s[1]
Declination	+10° 53′ 45.335″[1]
Apparent magnitude (V)	6.20±0.01[2]
B
Right ascension	20h 30m 17.9505s[3]
Declination	+10° 53′ 46.244″[3]
Apparent magnitude (V)	8.00±0.01[2]
Characteristics
Spectral type	A1:III shell[4]
U−B color index	−0.11[5]
B−V color index	−0.03[5]
Astrometry
Radial velocity (Rv)	−15.5 ± 2[6] km/s
Absolute magnitude (MV)	−0.69[7]
A
Proper motion (μ)	RA: +19.320 mas/yr[1] Dec.: +4.645 mas/yr[1]
Parallax (π)	4.6400 ± 0.0616 mas[1]
Distance	703 ± 9 ly (216 ± 3 pc)
B
Proper motion (μ)	RA: +19.545[3] mas/yr Dec.: +4.710[3] mas/yr
Parallax (π)	4.1851 ± 0.1421 mas[3]
Distance	780 ± 30 ly (239 ± 8 pc)
Details
A
Mass	3.1±0.3[8] M☉
Surface gravity (log g)	3.66±0.77[8] cgs
Temperature	10,651+932 −1156[8] K
Metallicity [Fe/H]	0.00[9] dex
Rotational velocity (v sin i)	217[10] km/s
Age	246[9] Myr
B
Surface gravity (log g)	4.14+0.19 −0.47[8] cgs
Rotational velocity (v sin i)	370[10] km/s
Other designations
1 Delphini, BD+10°4303, HD 195325, HIP 101160, HR 7836, SAO 106172, WDS J20303+1054AB
Database references
SIMBAD	data

1 Del consists of three components. The brightest of them has a magnitude of 6.1; a companion located around 0.9 arcseconds from the primary has an apparent magnitude of 8.1; and a third star, located much farther away at around 17 arcseconds from component A, is the faintest with a magnitude of around 14 and is an unrelated background object.[11]

The entire system has a stellar classification of A1: III sh, indicating that it is a white giant + a shell star. However, there is some uncertainty about the temperature class. When resolved, the secondary has a class of B9. 1 Del A has 3 times the mass of the Sun and an effective temperature of 10,651 K,[8] giving it a bluish white glow. It is estimated to be almost 250 million years old and has a solar metallicity.[9] Both components spin rapidly, with projected rotational velocities of 217 and 370 km/s respectively.[10] As for the peculiarities, the shell star is a primary component; the spectrum of the secondary shows broad absorption lines.[10]

Due to the stability of the emission lines data from 1 Delphini has been used for developing models of shell stars and Be stars.[10]

References

Further reading

Merrill, Paul W.; Burwell, Cora G. (November 1949). "Second Supplement to the Mount Wilson Catalogue and Bibliography of Stars of Classes B and a whose Spectra have Bright Hydrogen Lines". The Astrophysical Journal. 110: 387. Bibcode:1949ApJ...110..387M. doi:10.1086/145215. eISSN 1538-4357. ISSN 0004-637X.

Merrill, Paul W. (January 1952). "Spectra of Two Stars with Stable Shells". The Astrophysical Journal. 115: 42. Bibcode:1952ApJ...115...42M. doi:10.1086/145507. eISSN 1538-4357. ISSN 0004-637X.

van den Bos, W. H. (February 1958). "Micrometer measures of double stars". The Astronomical Journal. 63: 63. Bibcode:1958AJ.....63...63V. doi:10.1086/107694. ISSN 0004-6256.

Ringuelet-Kaswalder, Adela E. (August 1963). "Shell Stars and Rotationally Unstable Be Stars". Publications of the Astronomical Society of the Pacific. 75: 323. Bibcode:1963PASP...75..323R. doi:10.1086/127960. eISSN 1538-3873. ISSN 0004-6280.

Gray, David F.; Marlborough, J. M. (March 1974). "Photoelectric Profile Measurements of Halpha and Hbeta in be Stars". The Astrophysical Journal Supplement Series. 27: 121. Bibcode:1974ApJS...27..121G. doi:10.1086/190291. eISSN 1538-4365. ISSN 0067-0049.