Phi Sagittarii

Phi Sagittarii
Location of φ Sagittarii (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Sagittarius
Right ascension 18h 45m 39.38610s[1]
Declination −26° 59′ 26.7944″[1]
Apparent magnitude (V) 3.17[2]
Characteristics
Spectral type B8.5 III[3]
U−B color index −0.36[4]
B−V color index −0.11[4]
Astrometry
Radial velocity (Rv)+21.5[2] km/s
Proper motion (μ) RA: +50.61[1] mas/yr
Dec.: +1.22[1] mas/yr
Parallax (π)13.63 ± 0.19 mas[1]
Distance239 ± 3 ly
(73 ± 1 pc)
Absolute magnitude (MV)−1.16[5]
Details
Mass3.41[6] M☉
Radius4.8[7] R☉
Luminosity475[7] L☉
Surface gravity (log g)3.73[6] cgs
Temperature12,487±425[6] K
Rotational velocity (v sin i)46[6] km/s
Age152[6] Myr
Other designations
Namalsadirah 1, Awal al Sadira, φ Sgr, Phi Sgr, 27 Sagittarii, CPD−27  5241, FK5 1487, GC 25661, HD 173300, HIP 92041, HR 7039, SAO 268859, PPM 297231[8]
Database references
SIMBADdata

Phi Sagittarii, Latinized from φ Sagittarii, is an interferometric binary star in the southern constellation of Sagittarius. With an apparent visual magnitude of 3.17,[2] it is the ninth-brightest star in the constellation and is readily visible to the naked eye. Parallax measurements place it at a distance of roughly 239 light-years (73 parsecs) from the Earth.[1] It is receding with a radial velocity of +21.5 km/s.[2]

The stellar classification of this star has been rated at B8.5 III,[3] with the luminosity class of III indicating it is a giant star evolved away from the main sequence after it has exhausted the hydrogen at its core. This energy is being radiated from the star's outer envelope at an effective temperature of 12487 K,[6] which produces the blue-white hue typical of B-type stars.[9]

This star has been catalogued as a spectroscopic binary[10] and a companion was apparently detected through lunar occultation.[11] However, the latter was pointed out as spurious.[7][12] Interferometric observations taken in 2017 finally revealed that Phi Sgr is indeed a binary by resolving a companion with a near-infrared K band flux ratio of 6% (corresponding to a mass of 1.6 M☉) at a separation of 17.7 mas (1.3 au).[13]

  1. ^ a b c d e f Cite error: The named reference aaa474_2_653 was invoked but never defined (see the help page).
  2. ^ a b c d Cite error: The named reference scfs was invoked but never defined (see the help page).
  3. ^ a b Cite error: The named reference houk1979 was invoked but never defined (see the help page).
  4. ^ a b Cite error: The named reference clpl4_99 was invoked but never defined (see the help page).
  5. ^ Cite error: The named reference Anderson2012 was invoked but never defined (see the help page).
  6. ^ a b c d e f Cite error: The named reference David_Hillenbrand_2015 was invoked but never defined (see the help page).
  7. ^ a b c Cite error: The named reference kaler was invoked but never defined (see the help page).
  8. ^ Cite error: The named reference SIMBAD was invoked but never defined (see the help page).
  9. ^ Cite error: The named reference csiro was invoked but never defined (see the help page).
  10. ^ Lee, O. J. (1910-11-01). "Measures on nineteen new spectroscopic binaries". The Astrophysical Journal. 32: 300–308. Bibcode:1910ApJ....32..300L. doi:10.1086/141806. ISSN 0004-637X.
  11. ^ Cite error: The named reference aj56 was invoked but never defined (see the help page).
  12. ^ Cite error: The named reference mnras389_2_869 was invoked but never defined (see the help page).
  13. ^ Waisberg, Idel; Klein, Ygal; Katz, Boaz (2023-05-16). "Hidden Companions to Intermediate-mass Stars. III. Discovery of a 1.6M ⊙, 1.3 au Companion to HIP 92041 = ϕ Sagittarii*". Research Notes of the AAS. 7 (5): 95. Bibcode:2023RNAAS...7...95W. doi:10.3847/2515-5172/acd4bf. ISSN 2515-5172.