V725 Sagittarii

V725 Sagittarii

A visual band light curve for V725 Sagittarii, adapted from Percy (2020)[1]
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Sagittarius
Right ascension 18h 11m 59.43904s[2]
Declination −36° 06′ 40.3345″[2]
Characteristics
Spectral type K4III (in 2009)[3]
Variable type Unique[4]
Astrometry
Proper motion (μ) RA: −1.111[2] mas/yr
Dec.: −4.396[2] mas/yr
Parallax (π)0.1572 ± 0.0433 mas[2]
Distanceapprox. 21,000 ly
(approx. 6,000 pc)
Absolute magnitude (MV)−2.4[3]
Details
Mass4.25+0.67
−2.40[5] M☉
Temperature4,413[5] K
Metallicity [Fe/H]−0.001[5] dex
Other designations
Database references
SIMBADdata

V725 Sagittarii is a variable star in the southern constellation of Sagittarius. As recently as a century ago, it was a Population II Cepheid; its transformation was documented by Henrietta Swope beginning in 1937,[7] and is one of the most exciting and instructive events in variable-star astronomy.[8] The star has varied between apparent visual magnitude 12.3 and 14.3.[4]

Prior to 1926, this star showed the appearance of being an irregular variable. It then became a Population II Cepheid showing a regular light curve with a period of 12 days. Monitoring showed a gradual increase to a 21 day period by 1935,[7] but did not show a corresponding change in brightness. The star was mostly ignored until 1967–68 when it was seen to vary by 0.4 magnitude with a 50 day period.[8] Steady observation thereafter showed that the star had experienced a thermal flash and performed a loop on the H-R diagram. It migrated from the asymptotic giant branch (AGB) to the Cepheid instability strip and then back to the AGB.[3]

In 1973, the spectral class of V725 Sagittarii was estimated to be between F8 and G2 and similar to a type Ib supergiant.[3] In 1994 it was observed to be G8 based on the spectral lines of metals and later than F8 based on the hydrogen lines.[9] In 2006, it was reported that in 2000 V725 Sagittarii was an early M star with emission lines.[10] In 2010, the spectral type was estimated from its colours and other properties to be K4III, although possibly late K.[3]

  1. ^ Cite error: The named reference PercyJAVSO was invoked but never defined (see the help page).
  2. ^ a b c d e Cite error: The named reference GaiaDR2 was invoked but never defined (see the help page).
  3. ^ a b c d e Cite error: The named reference Battinelli_Demers_2010 was invoked but never defined (see the help page).
  4. ^ a b Cite error: The named reference Samus_et_al_2017 was invoked but never defined (see the help page).
  5. ^ a b c Cite error: The named reference starhorse was invoked but never defined (see the help page).
  6. ^ Cite error: The named reference SIMBAD was invoked but never defined (see the help page).
  7. ^ a b Cite error: The named reference Swope1937 was invoked but never defined (see the help page).
  8. ^ a b Cite error: The named reference Demers1973 was invoked but never defined (see the help page).
  9. ^ Cite error: The named reference harris1984 was invoked but never defined (see the help page).
  10. ^ Cite error: The named reference percy2006 was invoked but never defined (see the help page).