R Sagittae

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R Sagittae
RSgeLightCurve.png
A visual band light curve for R Sagittae, plotted from ASAS data [1]
Observation data
Epoch J2000.0        Equinox J2000.0 (ICRS)
Constellation Sagitta
Right ascension 20h 14m 03.7451s [2]
Declination +16° 43′ 35.053″ [2]
Apparent magnitude  (V)8.9-9.8 [3]
Characteristics
Evolutionary stage Post-AGB
Spectral type G0Ib-G8Ib [3]
U−B color index +0.1-+0.9 [4]
B−V color index +0.75-+1.3 [4]
Variable type RVb [3]
Astrometry
Radial velocity (Rv)+8.3 [5]  km/s
Proper motion (μ)RA: −2.180 [6]   mas/yr
Dec.: −4.818 [6]   mas/yr
Parallax (π)0.4030 ± 0.0457  mas [6]
Distance approx. 8,100  ly
(approx. 2,500  pc)
Absolute magnitude  (MV)–3.505 [7]
Details
Mass 0.81 [7]   M☉
Radius 61.2+12.5
−9.9 [7]   R☉
Luminosity 2,329+744
−638 [7]   L☉
Surface gravity (log g)-0.5-0.0 [3]   cgs
Temperature 5,100 [7] (4,250-5,750 [3] )  K
Metallicity [Fe/H]-0.50 [3] [8]   dex
Other designations
HD  192388, BD  +16 4197, SAO  105871, AAVSO  2009+16
Database references
SIMBAD data

R Sagittae is an RV Tauri variable star in the constellation Sagitta that varies from magnitude 8.0 to 10.5 in 70.77 days. It is a post-AGB low mass yellow supergiant that varies between spectral types G0Ib and G8Ib as it pulsates. Its variable star designation of "R" indicates that it was the first star discovered to be variable in the constellation. It was discovered in 1859 by Joseph Baxendell, though classified as a semi regular variable until RV Tauri variables were identified as a distinct class in 1905. [9]

R Sagittae is classified as an RV Tauri variable because of the distinctive regular variations with alternating deep and shallow minima. The period is conventionally quoted as the time between two deep minima and is the fundamental pulsation mode. The shallow minimum is the result of a first overtone pulsation. It is further classified as RVb since the average and maximum magnitude varies slowly over several years. The main period also varies over a period of decades. [4] It has around 90% the mass of the Sun and an average effective (surface) temperature of around 5000 K. [10] It is around 10,000 times as luminous as the Sun. [3] Measurement of its parallax by the Gaia satellite yields a distance of around 8,100 light-years. [6]

Variable star observer David Levy recommends that amateur observers monitor it once a week to observe changes in brightness. [11]

RV Tauri variables are post-AGB stars, originally similar to the Sun but now in the last stages of their lives. They are crossing the Cepheid instability strip as they lose their outer layers on the way to becoming a planetary nebula. Although their spectra and luminosities resemble supergiants, they are old low mass population II stars. A period-colour-luminosity relationship has been derived from observations of RV Tauri variables in the Large Magellanic Cloud that is closely related to the relationship for type II Cepheid variables. [12]

Related Research Articles

<span class="mw-page-title-main">Variable star</span> Star whose brightness fluctuates, as seen from Earth

A variable star is a star whose brightness as seen from Earth changes with time. This variation may be caused by a change in emitted light or by something partly blocking the light, so variable stars are classified as either:

<span class="mw-page-title-main">Mira variable</span> Type of variable star

Mira variables are a class of pulsating stars characterized by very red colours, pulsation periods longer than 100 days, and amplitudes greater than one magnitude in infrared and 2.5 magnitude at visual wavelengths. They are red giants in the very late stages of stellar evolution, on the asymptotic giant branch (AGB), that will expel their outer envelopes as planetary nebulae and become white dwarfs within a few million years.

<span class="mw-page-title-main">Long-period variable star</span> Cool luminous pulsating variable star

The descriptive term long-period variable star refers to various groups of cool luminous pulsating variable stars. It is frequently abbreviated to LPV.

<span class="mw-page-title-main">RV Tauri</span> Star in the constellation Taurus

RV Tauri is a star in the constellation Taurus. It is a yellow supergiant and is the prototype of a class of pulsating variables known as RV Tauri variables. It is a post-AGB star and a spectroscopic binary about 4,700 light years away.

<span class="mw-page-title-main">RV Tauri variable</span> Class of luminous variable star

RV Tauri variables are luminous variable stars that have distinctive light variations with alternating deep and shallow minima.

<span class="mw-page-title-main">119 Tauri</span> Star in the constellation Taurus

119 Tauri is a red supergiant star in the constellation Taurus. It is a semiregular variable and its angular diameter has been measured at about 10 mas.

<span class="mw-page-title-main">RS Puppis</span> Variable star in the constellation Puppis

RS Puppis is a Cepheid variable star around 6,000 ly away in the constellation of Puppis. It is one of the biggest and brightest known Cepheids in the Milky Way galaxy and has one of the longest periods for this class of star at 41.5 days.

<span class="mw-page-title-main">Yellow supergiant</span> Star that has a supergiant luminosity class, with a spectral type of F or G

A yellow supergiant (YSG) is a star, generally of spectral type F or G, having a supergiant luminosity class. They are stars that have evolved away from the main sequence, expanding and becoming more luminous.

<span class="mw-page-title-main">Type II Cepheid</span>

Type II Cepheids are variable stars which pulsate with periods typically between 1 and 50 days. They are population II stars: old, typically metal-poor, low mass objects.

<span class="mw-page-title-main">R Scuti</span> Variable star in the constellation Scutum

R Scuti is a star in the constellation of Scutum. It is a yellow supergiant and is a pulsating variable known as an RV Tauri variable. It was discovered in 1795 by Edward Pigott at a time when only a few variable stars were known to exist.

<span class="mw-page-title-main">Classical Cepheid variable</span>

Classical Cepheids are a type of Cepheid variable star. They are young, population I variable stars that exhibit regular radial pulsations with periods of a few days to a few weeks and visual amplitudes ranging from a few tenths of a magnitude up to about 2 magnitudes. Classical Cepheids are also known as Population I Cepheids, Type I Cepheids, and Delta Cepheid variables.

<span class="mw-page-title-main">S Crucis</span> Variable star in the constellation Crux

S Crucis is a star in the constellation Crux. A Cepheid variable, its apparent magnitude ranges from 6.22 to 6.92 over 4.68997 d. It is a yellow-white supergiant that pulsates between spectral types F6Ib-II and G1Ib-II.

<span class="mw-page-title-main">S Vulpeculae</span> Variable star in the constellation Vulpecula

S Vulpeculae is a variable star located in the constellation Vulpecula. A supergiant star, it is around 382 times the diameter of the Sun.

<span class="mw-page-title-main">AC Herculis</span> Spectroscopic binary star in the constellation Hercules

AC Herculis, is an RV Tauri variable and spectroscopic binary star in the constellation of Hercules. It varies in brightness between apparent magnitudes 6.85 and 9.0.

<span class="mw-page-title-main">HP Lyrae</span> Variable star in the constellation Lyra

HP Lyrae is a variable star in the constellation Lyra, with a visual magnitude varying between 10.2 and 10.8. It is likely to be an RV Tauri variable, an unstable post-AGB star losing mass before becoming a white dwarf.

<span class="mw-page-title-main">Y Lyncis</span> Variable star in the constellation Lynx

Y Lyncis is a semiregular variable star in the constellation Lynx. It is an asymptotic giant branch star of spectral type M6S, with a luminosity class of Ib, indicating a supergiant luminosity. It is around 1,160 light years away.

<span class="mw-page-title-main">U Monocerotis</span> Variable star system in the constellation Monoceros

U Monocerotis is a pulsating variable star and spectroscopic binary in the constellation Monoceros. The primary star is an RV Tauri variable, a cool luminous post-AGB star evolving into a white dwarf.

<span class="mw-page-title-main">XX Persei</span> Star in the constellation Perseus

XX Persei is a semiregular variable red supergiant star in the constellation Perseus, between the Double Cluster and the border with Andromeda.

<span class="mw-page-title-main">SX Centauri</span> Supergiant variable star in the constellation Centaurus

SX Centauri is a variable star in the constellation Centaurus. An RV Tauri variable, its light curve alternates between deep and shallow minima, varying its apparent magnitude from 9.1 to 12.4. From the period-luminosity relationship, it is estimated to be around 1.6 kpc from Earth. Gaia Data Release 2 gives a parallax of 0.2175 mas, corresponding to distance of about 4,600 pc.

<span class="mw-page-title-main">SZ Tauri</span>

SZ Tauri is a variable star in the equatorial constellation of Taurus. The brightness of this star varies from an apparent visual magnitude of 6.39 down to 6.69 with a period of 3.149 days, which is near the lower limit of visibility to the naked eye. The distance to this star is approximately 2,070 light years based on parallax measurements. There is some indication this may be a binary system, but the evidence is inconclusive.

References

  1. ↑ "ASAS All Star Catalogue". The All Sky Automated Survey. Retrieved 8 December 2021.
  2. 1 2 Hog, E.; Kuzmin, A.; Bastian, U.; Fabricius, C.; Kuimov, K.; Lindegren, L.; Makarov, V. V.; Roeser, S. (1998). "The TYCHO Reference Catalogue". Astronomy and Astrophysics. 335: L65. Bibcode:1998A&A...335L..65H.
  3. 1 2 3 4 5 6 7 Gonzalez, Guillermo; Lambert, David L.; Giridhar, Sunetra (1997). "Abundance Analyses of the Field RV Tauri Variables: EP Lyrae, DY Orionis, AR Puppis, and R Sagittae". The Astrophysical Journal. 479 (1): 427–440. Bibcode:1997ApJ...479..427G. doi: 10.1086/303852 .
  4. 1 2 3 Zsoldos, E. (1993). "Photometry of yellow semiregular variables - AC Herculis, R Sagittae and V Vulpeculae". Astronomy and Astrophysics. 268: 149. Bibcode:1993A&A...268..149Z.
  5. ↑ Wilson, Ralph Elmer (1953). "General catalogue of stellar radial velocities". Washington: 0. Bibcode:1953GCRV..C......0W.
  6. 1 2 3 4 Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics . 616. A1. arXiv: 1804.09365 . Bibcode: 2018A&A...616A...1G . doi: 10.1051/0004-6361/201833051 . Gaia DR2 record for this source at VizieR.
  7. 1 2 3 4 5 Bódi, A.; Kiss, L. L. (2019). "Physical properties of galactic RV Tauri stars from Gaia DR2 data". The Astrophysical Journal. 872 (1): 60. arXiv: 1901.01409 . Bibcode:2019ApJ...872...60B. doi: 10.3847/1538-4357/aafc24 . S2CID   119099605.
  8. ↑ Wahlgren, Glenn M. (1992). "The metallicity and luminosity of RV Tauri variables from medium-resolution spectra". Astronomical Journal. 104: 1174. Bibcode:1992AJ....104.1174W. doi:10.1086/116306.
  9. ↑ Gerasimovič, B.P. (1929). "Investigations of Semiregular Variables. VI. A General Study of RV Tauri Variables". Harvard College Observatory Circular. 341: 1–15. Bibcode:1929HarCi.341....1G.
  10. ↑ Stasińska, G.; Szczerba, R.; Schmidt, M.; Siódmiak, N. (2006). "Post-AGB stars as testbeds of nucleosynthesis in AGB stars". Astronomy and Astrophysics. 450 (2): 701–714. arXiv: astro-ph/0601504 . Bibcode:2006A&A...450..701S. doi:10.1051/0004-6361:20053553. S2CID   12040452.
  11. ↑ Levy, David H. (1998). Observing Variable Stars: A Guide for the Beginner. Cambridge, United Kingdom: Cambridge University Press. pp. 152–53. ISBN   978-0-521-62755-9.
  12. ↑ Pollard, K. R.; Alcock, C.; Allsman, R. A.; Alves, D.; Axelrod, T. S.; Becker, A. C.; Bennett, D. P.; Cook, K. H.; Freeman, K. C.; Griest, K.; Lehner, M. J.; Marshall, S. L.; Peterson, B. A.; Pratt, M. R.; Quinn, P. J.; Sutherland, W.; Tomaney, A.; Welch, D. L.; MACHO Collaboration (2000). "RV Tauri Stars and Type II Cepheids in the Magellanic Clouds -- Results from the MACHO Database". The Impact of Large-Scale Surveys on Pulsating Star Research. 203: 89. Bibcode:2000ASPC..203...89P.
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