Delta1 Telescopii

Delta¹ Telescopii is a blue-white-hued binary star^[5] system in the southern constellation of Telescopium. It is faintly visible to the naked eye, having an apparent visual magnitude of 4.94.^[2] Based upon an annual parallax shift of 4.61 mas as seen from Earth,^[1] this system is roughly 710 light-years from the Sun. At that distance, the visual magnitude is diminished by an extinction factor of 0.29 due to interstellar dust.^[4]

For other stars with this Bayer designation, see δ Telescopii.

Delta¹ Telescopii

Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Telescopium
Right ascension	18h 31m 45.43288s[1]
Declination	−45° 54′ 53.3166″[1]
Apparent magnitude (V)	4.94[2]
Characteristics
Evolutionary stage	subgiant[3]
Spectral type	B6 IV[3]
U−B color index	−0.438[2]
B−V color index	−0.121[2]
Astrometry
Proper motion (μ)	RA: −3.75[1] mas/yr Dec.: −27.43[1] mas/yr
Parallax (π)	4.61±0.19 mas[1]
Distance	710 ± 30 ly (217 ± 9 pc)
Absolute magnitude (MV)	−0.74[4]
Orbit[5]
Period (P)	18.8456 d
Eccentricity (e)	0.51
Periastron epoch (T)	2435003.693 JD
Argument of periastron (ω) (secondary)	78°
Semi-amplitude (K1) (primary)	65.0 km/s
Details
δ1 Tel A
Mass	4.52±0.06[3] M☉
Radius	4.7[6] R☉
Luminosity	899[3] L☉
Temperature	12,417[3] K
Rotational velocity (v sin i)	11[3] km/s
Age	178[4] Myr
Other designations
δ1 Tel, CD−45°12550, HD 170465, HIP 90830, HR 6934, SAO 229092[7]
Database references
SIMBAD	data

This system is a single-lined spectroscopic binary with an orbital period of 18.8 days and an eccentricity of 0.51.^[5] The estimated size of the semimajor axis has a minimum of 14.5×10⁶ km, with the uncertainty due to lack of a value for the orbital inclination.^[8] The primary, component A, has a stellar classification of B6 IV,^[3] suggesting it is an evolving B-type subgiant star. Delta¹ Telescopii has an estimated 4.5^[3] times the mass of the Sun and about 4.7^[6] times the Sun's radius. It is radiating 899^[3] times the solar luminosity from its photosphere at an effective temperature of 12,417 K.^[3]