RY Sagittarii

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RY Sagittarii
Sagittarius constellation map.svg
Red circle.svg
Location of RY Sagittarii (circled)
Observation data
Epoch J2000.0 ICRS        Equinox J2000.0 ICRS
Constellation Sagittarius
Right ascension 19h 16m 32.76686s [1]
Declination −33° 31′ 20.3402″ [1]
Apparent magnitude  (V)5.8-14.0 [2]
Characteristics
Spectral type G0Iaep (C1,0) [2]
Variable type R CrB [2]
Astrometry
Radial velocity (Rv)−16.02 [1]  km/s
Proper motion (μ)RA: 8.957 [1]   mas/yr
Dec.: −0.277 [1]   mas/yr
Parallax (π)0.5880 ± 0.0273 [1]   mas
Distance 5,500 ± 300  ly
(1,700 ± 80  pc)
Absolute magnitude  (MV)−5 [3]
Details
Radius 60 [3]   R☉
Luminosity 9,120 [3]   L☉
Temperature 7,250 [4]   K
Other designations
RY Sgr, CD−33 14076, HD  180093, HIP  94730, HR  7296, SAO  211117
Database references
SIMBAD data

RY Sagittarii is a yellow supergiant and an R Coronae Borealis type variable star in the constellation Sagittarius. Although it ostensibly has the spectrum of a G-type star, it differs markedly from most in that it has almost no hydrogen and much carbon.

Contents

Discovery

RY Sgr light curve RYSgr lightcurve.png
RY Sgr light curve

Colonel Ernest Elliott Markwick first came across what became known as RY Sagittarii during searches for variable stars while posted in Gibraltar. [5] He recorded it dimming from magnitude 7 in July 1893 to fainter than 11 by 23 October that year, and brightening to magnitude 6.4 by November 1894. [6] Edward Charles Pickering wrote that it was a "remarkable object", [6] and "nearly got away". [5] The spectrum was first noted to be peculiar at the time, [6] and by 1953 it was classified as a R Coronae Borealis variable, along with a handful of other stars. [7]

Mystified by its origins, Danziger postulated possible explanations as forming from a helium cloud, an aged star that had exhausted its hydrogen, or a star that had somehow thrown off its hydrogen envelope, though noted there was no evidence of such an envelope. He conceded that knowledge of star evolution was not advanced enough to come up with an explanation. [8]

Variability

It is one of the three brightest R Coronae Borealis stars visible to Earth observers, along with R Coronae Borealis and V854 Centauri, [9] and the brightest in the southern hemisphere. [3] It is also a pulsating variable, with a semiregular period of 38 days. [10] Its light curve has been studied for over a hundred years and is typical for the class, characterised by a sudden drop in brightness of several magnitudes over a few weeks before gradually brightening over the following several months. The timing between these dimmings is irregular. [10] The cause of the drop in magnitude is the presence of dust clouds of carbon obscuring (and most likely ejected from) the star, though the mechanism how this might occur is not known. [10] [11] Extensive clouds have been detected with ESO's Very Large Telescope Interferometer. [12]

Properties

The star is so remote that its parallax, distance and hence luminosity were impossible to calculate with any accuracy. [10] The Hipparcos satellite calculated its parallax at 1.29 milliarcseconds, [13] yielding a distance of 1,716.6 light-years (526.32 parsecs ) from Earth. Its parallax from the Gaia EDR3 is much smaller at 0.56  mas , indicating a much larger distance [1] consistent with non-parallax estimates of the distance. [3] The distance derived indirectly by comparison with similar stars, is around 2,000 parsecs. [3] Its effective temperature has been calculated at 7,250 K [4] and its size at 60 R☉ based on an assumed luminosity of 9,120 L☉. [3]

Related Research Articles

R Coronae Borealis

R Coronae Borealis is a low-mass yellow supergiant star in the constellation of Corona Borealis. It is the prototype of the R Cor Bor class of variable stars, which fade by several magnitudes at irregular intervals. R Coronae Borealis itself normally shines at approximately magnitude 6, just about visible to the naked eye, but at intervals of several months to many years fades to as faint as 15th magnitude. Over successive months it then gradually returns to its normal brightness, giving it the nickname "reverse nova", after the more common type of star which rapidly increases in brightness before fading.

KW Sagittarii is a red supergiant, located approximately 1,900 parsecs away from our Sun in the direction of the constellation Sagittarius. It is one of the largest known stars. If placed at the center of the Solar System, the star's surface would engulf Mars.

R Coronae Borealis variable

An R Coronae Borealis variable is an eruptive variable star that varies in luminosity in two modes, one low amplitude pulsation, and one irregular, unpredictably-sudden fading by 1 to 9 magnitudes. The prototype star R Coronae Borealis was discovered by the English amateur astronomer Edward Pigott in 1795, who first observed the enigmatic fadings of the star. Only about 150 RCB stars are currently known in our Galaxy while up to 1000 were expected, making this class a very rare kind of star.

S Coronae Borealis

S Coronae Borealis is a Mira variable star in the constellation Corona Borealis. Its apparent magnitude varies between 5.8 and 14.1, with a period of 360 days—just under a year. Within the constellation, it lies to the west of Theta Coronae Borealis, and around 1 degree southeast of the eclipsing binary star U Coronae Borealis.

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, and is one of the most exciting and instructive events in variable-star astronomy. The star has varied between apparent visual magnitude 12.3 and 14.3.

U Aquarii, abbreviated U Aqr, is a variable star in the equatorial constellation of Aquarius. It is invisible to the naked eye, having an apparent visual magnitude that ranges from 10.6 down to as low as 15.9. Based on parallax measurements, the distance to this star is approximately 38 kly (12 kpc). In 1990, W. A. Lawson and associates provided a distance estimate of 43 kly (13.2 kpc) based on the assumption of a bolometric magnitude of −5. It appears to lie several kiloparsecs below the galactic plane, and thus may belong to an old stellar population.

HD 168607 Star in the constellation Sagittarius

HD 168607 is a blue hypergiant and luminous blue variable (LBV) star located in the constellation of Sagittarius, easy to see with amateur telescopes. It forms a pair with HD 168625, also a blue hypergiant and possible luminous blue variable, that can be seen at the south-east of M17, the Omega Nebula.

HD 102350 is a single star in the constellation Centaurus. It has a yellow hue and is visible to the naked eye with an apparent visual magnitude of 4.11. The distance to this star is approximately 390 light years based on parallax, but it is drifting closer with a radial velocity of −3 km/s. It has an absolute magnitude of −1.51.

Gamma Coronae Borealis, Latinized from γ Coronae Borealis, is a binary star system in the northern constellation of Corona Borealis. It is visible to the naked eye with an apparent visual magnitude of 3.83. Based upon an annual parallax shift of 22.33 mas as seen from Earth, it is located about 146 light years from the Sun. The system is moving closer to the Sun with a radial velocity of about −15 km/s.

Theta Coronae Borealis, Latinized from θ Coronae Borealis, is a binary star system in the constellation Corona Borealis. It shines with a combined apparent visual magnitude of 4.13. There are two components: Theta Coronae Borealis A is of apparent magnitude 4.16, while Theta Coronae Borealis B lies around 1 arcsecond distant and has an apparent magnitude of 6.29. The system is located around 375 light-years from Earth, as estimated from its parallax of 8.69 milliarcseconds. It is estimated to be 85 million years old, with the primary star expected to remain on the main sequence burning its core hydrogen for another 75 million years and the secondary around 500 million years. Both stars will cool and expand once their core hydrogen is exhausted, becoming red giants.

Epsilon Coronae Borealis

Epsilon Coronae Borealis, Latinized from ε Coronae Borealis, is a multiple star system in the constellation Corona Borealis located around 230 light-years from the Solar System. It shines with a combined apparent magnitude of 4.13, meaning it is visible to the unaided eye in all night skies except those brightly lit in inner city locations. It is an orange giant around 1.7 times as massive as the Sun of spectral type K2III, which has exhausted its core fuel supply of hydrogen and swollen to 21 times the Sun's diameter and 151 times its luminosity. That is, Epsilon Coronae Borealis's diameter is about one-quarter of Mercury's orbit. Its surface temperature has been calculated to be 4365 ± 9 K, or 4406 ± 15 K. It is thought to be around 1.74 billion years old.

Delta Coronae Borealis, Latinized from δ Coronae Borealis, is a variable star in the constellation Corona Borealis. Its apparent magnitude varies regularly between apparent magnitude 4.57 and 4.69, and it is around 170 light-years distant.

Lambda Coronae Borealis

Lambda Coronae Borealis, its name Latinised from λ Coronae Borealis, is a single star in the northern constellation of Corona Borealis. In publications it is also identified as HR 5936 and HD 142908. It has a yellow-white hue and is dimly visible to the naked eye with an apparent visual magnitude of 5.43. The star is located at a distance of 136 light years based on parallax, but is drifting closer with a radial velocity of −12 km/s.

V1073 Scorpii

V1073 Scorpii is a variable star in the constellation Scorpius. It has a non-Greek Bayer designation of k Scorpii. The star has a blue-white hue and is visible to the naked eye with an apparent visual magnitude that fluctuates around +4.87. Parallax measurements yield a distance estimate of approximately 2,920 ly (896 pc) from the Sun, and it is drifting further away with a radial velocity of +7 km/s. It has an absolute magnitude of −6.8

UY Scuti star in the constellation Scutum

UY Scuti (BD-12°5055) is a red supergiant star in the constellation Scutum. It is considered one of the largest known stars by radius and is also a pulsating variable star, with a maximum brightness of magnitude 8.29 and a minimum of magnitude 10.56. It has an estimated radius of 1,708 solar radii (1.188×109 kilometres; 7.94 astronomical units), thus a volume nearly 5 billion times that of the Sun. It is approximately 2.9 kiloparsecs (9,500 light-years) from Earth. If placed at the center of the Solar System, its photosphere would at least engulf the orbit of Jupiter.

RS Telescopii, abbreviated RS Tel, is a variable star in the southern constellation of Telescopium. It is a dim star with an apparent visual magnitude of 10.67, which is much too faint to be visible without a telescope. The variability of this star was discovered by Evelyn F. Leland and announced by Edward C. Pickering in 1910. It was first studied by Cecilia H. Payne in 1928 at the Harvard College Observatory.

Nu<sup>1</sup> Coronae Borealis

Nu1 Coronae Borealis is a solitary, red-hued star located in the northern constellation of Corona Borealis. It is faintly visible to the naked eye, having an apparent visual magnitude of 5.20. Based upon an annual parallax shift of 5.0 mas, it is located roughly 650 light years from the Sun. At that distance, the visual magnitude is diminished by an extinction of 0.1 due to interstellar dust. This object is drifting closer with a radial velocity of −13 km/s.

Sigma Coronae Borealis is a star system in the constellation of Corona Borealis. It is a quintuple star system containing three sunlike main-sequence stars and two other low-mass stars. The combined visual magnitude is 5.3 and the system lies 74 light years from Earth. σ CrB A is the variable star TZ Coronae Borealis.

Upsilon Coronae Borealis, Latinized from υ Coronae Borealis, is a solitary star in the northern constellation of Corona Borealis. It is a white-hued star that is dimly visible to the naked eye with an apparent visual magnitude of 5.78. The distance to this object is approximately 630 light-years based on parallax.

S Apodis is an R Coronae Borealis variable star located in the far southern constellation Apus. These are extremely hydrogen-deficient supergiants thought to have arisen as the result of the merger of two white dwarfs; fewer than 100 have been discovered as of 2012. Located around 13,000 light-years distant, it shines with a luminosity approximately 960 times that of the Sun and has a surface temperature of 3916 K.

References

  1. 1 2 3 4 5 6 7 Brown, A. G. A.; et al. (Gaia collaboration) (2020). "Gaia Early Data Release 3: Summary of the contents and survey properties". Astronomy & Astrophysics . In press. arXiv: 2012.01533 . doi:10.1051/0004-6361/202039657. S2CID   227254300. Gaia EDR3 record for this source at VizieR.
  2. 1 2 3 "V RY Sgr". The International Variable Star Index. Retrieved 8 August 2013.
  3. 1 2 3 4 5 6 7 De Laverny, P.; Mékarnia, D. (2004). "First detection of dust clouds around R CrB variable stars". Astronomy and Astrophysics. 428: L13–L16. arXiv: astro-ph/0411735 . Bibcode:2004A&A...428L..13D. doi:10.1051/0004-6361:200400095. S2CID   15966263.
  4. 1 2 Clayton, Geoffrey C.; Geballe, T. R.; Zhang, Wanshu (2013). "Variable Winds and Dust Formation in R Coronae Borealis Stars". The Astronomical Journal. 146 (2): 9. arXiv: 1305.5047 . Bibcode:2013AJ....146...23C. doi:10.1088/0004-6256/146/2/23. S2CID   118385818. 23.
  5. 1 2 Shears, Jeremy (2011). "Ernest Elliott Markwick: Variable stars and military campaigns". The Journal of the British Astronomical Association. 122 (6): 335–48. arXiv: 1109.4234 . Bibcode:2012JBAA..122..335S.
  6. 1 2 3 Pickering, E. C. (1896). "Harvard College Observatory, Circular no. 7. Ten New Variable Stars". Astrophysical Journal. 4: 138–42. Bibcode:1896ApJ.....4..138P. doi:10.1086/140256.
  7. ↑ Bidelman, William P. (1953). "The Spectra of Certain Stars whose Atmospheres may BE Deficient in Hydrogen". Astrophysical Journal. 117: 25. Bibcode:1953ApJ...117...25B. doi:10.1086/145665.
  8. ↑ I. J., Danziger (1965). "A high-dispersion spectral study of RY Sagittarii". Monthly Notices of the Royal Astronomical Society . 130 (3): 199–221. Bibcode:1965MNRAS.130..199D. doi: 10.1093/mnras/130.3.199 .
  9. ↑ Skuljan, L.; Cottrell, P. L. (2002). "Recent declines of RS Telescopii, UW Centauri, and V Coronae Australis". The Observatory. 122: 322–29. Bibcode:2002Obs...122..322S.
  10. 1 2 3 4 Clayton, G. C. (1996). "The R Coronae Borealis Stars". Publications of the Astronomical Society of the Pacific. 108: 225. Bibcode:1996PASP..108..225C. doi: 10.1086/133715 .
  11. ↑ Davis, Kate (January 2000). "R Coronae Borealis". Variable Star of the Month. Retrieved 6 July 2014.
  12. ↑ de Laverny, Patrick (3 August 2007). "Star Caught Smoking: VLTI Snapshots Dusty Puff Around Variable Star". European Southern Observatory. Retrieved 13 March 2015.
  13. ↑ van Leeuwen, F. (November 2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653–664. arXiv: 0708.1752 . Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357. S2CID   18759600.
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