Wikipedia

EP Aquarii

EP Aquarii is a semiregular variable star in the equatorial constellation of Aquarius. At its peak brightness, visual magnitude 6.37,[3] it might be faintly visible to the unaided eye under ideal observing conditions. A cool red giant on the asymptotic giant branch (AGB), its visible light brightness varies by about 1/2 magnitude over a period of 55 days.[4][3] EP Aquarii has a complex circumstellar envelope (CSE), which has been the subject of numerous studies.[4][9][10][5][11]

EP Aquarii

A visual band light curve for EP Aqaurii, plotted from data published by Tabur et al. (2009)[1]
Observation data
Epoch J2000      Equinox J2000
Constellation Aquarius
Right ascension 21h 46m 31.84949s[2]
Declination −02° 12′ 45.9285″[2]
Apparent magnitude (V) 6.37 - 6.82[3]
Characteristics
Spectral type M8 III[4]
Variable type SRb[3]
Astrometry
Radial velocity (Rv)+33.98[5] km/s
Proper motion (μ) RA: +25.547[2] mas/yr
Dec.: +20.433[2] mas/yr
Parallax (π)7.7134 ± 0.4896 mas[2]
Distance420 ± 30 ly
(130 ± 8 pc)
Details
Mass1.7[4] M☉
Radius384[6] R☉
Luminosity4,800[4] L☉
Surface gravity (log g)−0.18[7] cgs
Temperature3,200[4] K
Metallicity [Fe/H]+0.50[7] dex
Other designations
BD−02°5631, FK5 3740, HD 207076, HIP 107516, SAO 145652[8]
Database references
SIMBADdata

The study of EP Aquarii's extended CSE began in 1984, when a spectral line arising from a rotational transition of carbon monoxide (CO) was detected by Zuckerman and Dyck, using the NRAO 12m telescope.[12] In the early 1990s, analysis of the IRAS satellite data showed the presence of an extended dust shell surrounding the star, with a radius of about 1 lightyear.[13][14] In the late 1990s, high spectral-resolution observations at the Caltech Submillimeter Observatory (CSO) showed that EP Aquarii's CO line profiles had an unusual shape that suggested the presence of two distinct stellar winds, expanding at dramatically different velocities: 1.4 and 11 km/sec.[15][11] In the early 2000s, observations of the 21 cm line of atomic hydrogen at the Nançay Radio Observatory confirmed the presence of a large circumstellar shell with multiple velocity components.[11]

The completion of Atacama Large Millimeter Array allowed EP Aquarii to be studied with far higher sensitivity and angular resolution than was available to earlier researchers. The very narrow emission feature (indicating an expansion rate of 1.4 km/sec) seen in the CSO spectra was found to arise from a spiral structure, nearly face-on to our line of sight, which suggested the presence of an unseen companion star.[5] The higher velocity wind arises from a bi-conical outflow, the pole of which is roughly aligned to our line of sight.

Which chemical compounds are found in the CSEs of AGB stars is largely determined by whether or not the stellar atmosphere contains more carbon than oxygen.[16] EP Aquarii's atmosphere contains more oxygen than carbon.[10]

References

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  1. ^ Tabur, V.; Bedding, T. R.; Kiss, L. L.; Moon, T. T.; Szeidl, B.; Kjeldsen, H. (December 2009). "Long-term photometry and periods for 261 nearby pulsating M giants". Monthly Notices of the Royal Astronomical Society. 400 (4): 1945–1961. arXiv:0908.3228. Bibcode:2009MNRAS.400.1945T. doi:10.1111/j.1365-2966.2009.15588.x. S2CID 15358380.
  2. ^ a b c d e Brown, A. G. A.; et al. (Gaia collaboration) (2021). "Gaia Early Data Release 3: Summary of the contents and survey properties". Astronomy & Astrophysics. 649: A1. arXiv:2012.01533. Bibcode:2021A&A...649A...1G. doi:10.1051/0004-6361/202039657. S2CID 227254300. (Erratum: doi:10.1051/0004-6361/202039657e). Gaia EDR3 record for this source at VizieR.
  3. ^ a b c d "EP Aqr". The International Variable Star Index. AAVSO. Retrieved 29 May 2022.
  4. ^ a b c d e f Homan, Ward; Cannon, Emily; Montargès, Miguel; Richards, Anita M. S.; Millar, Tom J.; Decin, Leen (October 2020). "A detailed view on the circumstellar environment of the M-type AGB star EP Aquarii I. High-resolution ALMA and SPHERE observations". Astronomy and Astrophysics. 642: A93. arXiv:2008.08394. Bibcode:2020A&A...642A..93H. doi:10.1051/0004-6361/202038255. S2CID 221172771.
  5. ^ a b c Homan, Ward; Richards, Anita; Decin, Leen; de Koter, Alex; Kervella, Pierre (August 2018). "An unusual face-on spiral in the wind of the M-type AGB star EP Aquarii". Astronomy and Astrophysics. 616: A34. arXiv:1804.05684. Bibcode:2018A&A...616A..34H. doi:10.1051/0004-6361/201832834. S2CID 119071036.
  6. ^ Kervella, Pierre; Arenou, Frédéric; Thévenin, Frédéric (2022). "Stellar and substellar companions from Gaia EDR3". Astronomy & Astrophysics. 657: A7. arXiv:2109.10912. Bibcode:2022A&A...657A...7K. doi:10.1051/0004-6361/202142146. S2CID 237605138.
  7. ^ a b Anders, F.; Khalatyan, A.; Chiappini, C.; Queiroz, A. B.; Santiago, B. X.; Jordi, C.; Girardi, L.; Brown, A. G. A.; Matijevic, G.; Monari, G.; Cantat-Gaudin, T.; Weiler, M.; Khan, S.; Miglio, A.; Carrillo, I.; Romero-Gómez, M.; Minchev, I.; de Jong, R. S.; Antoja, T.; Ramos, P.; Steinmetz, M.; Enke, H. (1 August 2019). "Photo-astrometric distances, extinctions, and astrophysical parameters for Gaia DR2 stars brighter than G = 18". Astronomy and Astrophysics. 628: A94. arXiv:1904.11302. Bibcode:2019A&A...628A..94A. doi:10.1051/0004-6361/201935765. ISSN 0004-6361. S2CID 131780028.
  8. ^ "EP Aqr". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 29 May 2022.
  9. ^ Hoai, D. T.; Nhung, P. T.; Tuan-Anh, P.; Darriulat, P.; Diep, P. N.; Le Bertre, T.; Phuong, N. T.; Thai, T. T.; Winters, J. M. (April 2019). "The morpho-kinematics of the circumstellar envelope around the AGB star EP Aqr". Monthly Notices of the Royal Astronomical Society. 484 (2): 1865–1888. arXiv:1901.00974. Bibcode:2019MNRAS.484.1865H. doi:10.1093/mnras/stz041.
  10. ^ a b Tuan-Anh, P.; Hoai, D. T.; Nhung, P. T.; Darriulat, P.; Diep, P. N.; Le Bertre, T.; Phuong, N. T.; Thai, T. T.; Winters, J. M. (July 2019). "Observation of narrow polar jets in the nascent wind of oxygen-rich AGB star EP Aqr". Monthly Notices of the Royal Astronomical Society. 487 (1): 622–639. arXiv:1905.02715. Bibcode:2019MNRAS.487..622T. doi:10.1093/mnras/stz1281.
  11. ^ a b c Le Bertre, T.; Gérard, E. (May 2004). "The circumstellar environments of EP Aqr and Y CVn probed by the H I emission at 21 cm". Astronomy and Astrophysics. 419 (2): 549–561. Bibcode:2004A&A...419..549L. doi:10.1051/0004-6361:20035797.
  12. ^ Zuckerman, B.; Dyck, H. M. (May 1986). "Carbon Monoxide Emission from Stars in the IRAS and Revised AFGL Catalogs. I. Mass Loss Driven by Radiation Pressure on Dust Grains". The Astrophysical Journal. 304: 394–400. Bibcode:1986ApJ...304..394Z. doi:10.1086/164173.
  13. ^ Young, K.; Phillips, T. G.; Knapp, G. R. (June 1993). "Circumstellar Shells Resolved in the IRAS Survey Data. I. Data Processing Procedure, Results, and Confidence Tests". The Astrophysical Journal Supplement Series. 86: 517–540. Bibcode:1993ApJS...86..517Y. doi:10.1086/191789.
  14. ^ Young, K.; Phillips, T. G.; Knapp, G. R. (June 1993). "Circumstellar Shells Resolved in IRAS Survey Data. II. Analysis". The Astrophysical Journal. 409: 725–738. Bibcode:1993ApJ...409..725Y. doi:10.1086/172702.
  15. ^ Knapp, G. R.; Young, K.; Lee, E.; Jorissen, A. (July 1998). "Multiple Molecular Winds in Evolved Stars. I. A Survey of CO(2-1) and CO(3-2) Emission from 45 Nearby Asymptotic Giant Branch Stars". The Astrophysical Journal Supplement Series. 117 (1): 209–231. arXiv:astro-ph/9711125. Bibcode:1998ApJS..117..209K. doi:10.1086/313111. S2CID 15210237.
  16. ^ Iben, Icko; Renzini, Alvio (1983). "Asymptotic giant branch evolution and beyond". Annual Review of Astronomy and Astrophysics. 21: 271–342. Bibcode:1983ARA&A..21..271I. doi:10.1146/annurev.aa.21.090183.001415. Retrieved 31 May 2022.
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