EP Aquarii

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EP Aquarii
EPAqrLightCurve.png
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]
Distance 420 ± 30  ly
(130 ± 8  pc)
Details
Mass 1.7 [4]   M☉
Radius 384 [6]   R☉
Luminosity 4,800 [4]   L☉
Surface gravity (log g)−0.18 [7]   cgs
Temperature 3,200 [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
SIMBAD data

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]

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]

Related Research Articles

<span class="mw-page-title-main">Delta Aquarii</span> Star in the constellation Aquarius

Delta Aquarii, officially named Skat, is the third-brightest star in the constellation of Aquarius. The apparent visual magnitude is 3.3, which can be seen with the naked eye. The distance to this star is about 113 light-years based upon parallax measurements, and it has a close companion.

<span class="mw-page-title-main">Beta Aquarii</span> Double star in the constellation Aquarius

Beta Aquarii is a single star in the constellation of Aquarius. It has the official name Sadalsuud and the Bayer designation β Aquarii, abbreviated Beta Aqr or β Aqr. Based upon parallax measurements obtained during the Hipparcos mission, this component is located at a distance of approximately 540 light years (165 parsecs) from the Sun. It is drifting further away with a radial velocity of 6.5 km/s. The star serves as an IAU radial velocity standard.

<span class="mw-page-title-main">Lambda Aquarii</span> Star in the constellation Aquarius

Lambda Aquarii, informally known as Hydor, is a variable star in the equatorial constellation of Aquarius. The name is Latinized from the Bayer designation λ Aquarii. The apparent visual magnitude of this star ranges from 3.57 down to 3.80, which is bright enough to be visible with the naked eye. It lies just 0.39 degrees south of the ecliptic and so is subject to lunar occultations. The star is eclipsed by the sun from about 1-4 March; thus the star can be viewed the whole night, crossing the sky, in early September, in the current epoch. Lambda Aquarii is located at a distance of approximately 310 light-years (95 pc) from the Sun based on parallax, but is drifting closer with a radial velocity of −10.5 km/s.

Tau<sup>1</sup> Aquarii Star in the constellation Aquarius

Tau1 Aquarii, Latinized from τ1 Aquarii, is the Bayer designation for a single star in the equatorial constellation of Aquarius. With an apparent visual magnitude of 5.66, it is a faint naked eye that requires dark suburban skies for viewing. Parallax measurements made during the Hipparcos mission yield a distance estimate of roughly 355 light-years from Earth. The star is drifting further away with a radial velocity of +15 km/s. It is a candidate member of the Pisces-Eridanus stellar stream.

<span class="mw-page-title-main">Mu Aquarii</span> Binary star system in the constellation Aquarius

Mu Aquarii, Latinized from μ Aquarii, is the Bayer designation for a binary star system in the equatorial constellation of Aquarius. It is visible to the naked eye with a combined apparent visual magnitude of 4.7. Based upon parallax measurements, the distance to this system is about 157 light-years. It is drifting closer to the Sun with a radial velocity of −9.1 km/s.

<span class="mw-page-title-main">Upsilon Aquarii</span> Star in the constellation Aquarius

Upsilon Aquarii, Latinized from υ Aquarii, is the Bayer designation for a binary star system in the equatorial constellation of Aquarius. It is visible to the naked eye as a faint star with an apparent visual magnitude of 5.21. Parallax measurements give a distance estimate of 74.8 light-years from Earth. This is a high proper-motion star that is drifting closer to the Sun with a radial velocity of –2.3 km/s. It is part of the Hercules-Lyra association.

<span class="mw-page-title-main">Rho Aquarii</span> Star in the constellation Aquarius

Rho Aquarii, Latinized from ρ Aquarii, is the Bayer designation for a binary star system in the equatorial constellation of Aquarius. It is visible to the naked eye with an apparent visual magnitude of +5.34. Based upon parallax measurements, this star is at a distance of roughly 870 light-years from Earth. It is drifting closer with a radial velocity of –9 km/s. The proximity of this star to the ecliptic means it is subject to lunar occultations.

<span class="mw-page-title-main">3 Aquarii</span> Star in the constellation Aquarius

3 Aquarii is a variable star in the equatorial constellation of Aquarius. 3 Aquarii is the Flamsteed designation; it also bears the Bayer designation k Aquarii and the variable star designation EN Aquarii. With a mean apparent visual magnitude of 4.429, it is visible to the naked eye in dark skies. It has an annual parallax shift of 5.57 milliarcseconds with a 5% margin of error, which translates to a physical distance of around 590 light-years from Earth.

94 Aquarii is a triple star system in the equatorial constellation of Aquarius. 94 Aquarii is the Flamsteed designation. The brightest member has an apparent visual magnitude of 5.19, making it visible to the naked eye. The parallax measured by the Gaia spacecraft yields a distance estimate of around 73 light-years from Earth.

<span class="mw-page-title-main">106 Aquarii</span> Star in the constellation Aquarius

106 Aquarii, abbreviated 106 Aqr, is a single star in the equatorial constellation of Aquarius. 106 Aquarii is the Flamsteed designation, and it also bears the Bayer designation i1 Aquarii. It has an apparent visual magnitude of +5.2, making it bright enough to be viewed from the suburbs according to the Bortle Dark-Sky Scale. An annual parallax shift of 8.61 milliarcseconds yields an estimated distance of around 380 light-years from Earth.

5 Aquarii is a single star in the zodiac constellation of Aquarius, located about 830 light years away from the Sun, based on parallax. 5 Aquarii is the Flamsteed designation. It is visible to the naked eye as a faint, blue-white hued star with an apparent visual magnitude of 5.55. This object is moving closer to the Earth with a heliocentric radial velocity of −3 km/s.

82 Aquarii is a star in the equatorial constellation of Aquarius. 82 Aquarii is its Flamsteed designation. It has an apparent visual magnitude of 6.15, which, according to the Bortle Dark-Sky Scale, means it is a faint star that requires dark rural skies to view. The annual parallax shift of 82 Aquarii is 3.6764±0.1715 mas, which equates to a distance of roughly 890 light-years from Earth. Because this star is positioned near the ecliptic, it is subject to lunar eclipses.

<span class="mw-page-title-main">La Superba</span> Variable star in the constellation Canes Venatici

La Superba is a strikingly red giant star in the constellation Canes Venatici. It is a carbon star and semiregular variable.

<span class="mw-page-title-main">R Aquarii</span> Star in the constellation of Aquarius

R Aquarii is a variable star in the constellation Aquarius.

<span class="mw-page-title-main">T Cephei</span> Star in the constellation Cepheus

T Cephei is a Mira variable star in the constellation Cepheus. Located approximately 600 light-years distant, it varies between magnitudes 5.2 and 11.3 over a period of around 388 days.

<span class="mw-page-title-main">U Aquarii</span> Star in the constellation of Aquarius

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.

<span class="mw-page-title-main">S Canis Minoris</span> Variable star in the constellation Canis Minor

S Canis Minoris is a variable star in the equatorial constellation Canis Minor. It has a peak apparent visual magnitude of 6.5, so not normally visible to the naked eye. The star is located at a distance of approximately 1,360 light-years from the Sun based on stellar parallax, and is drifting further away with a radial velocity of about +68 km/s.

<span class="mw-page-title-main">W Aquilae</span> Variable star in the constellation Aquila

W Aquilae is a variable star in the constellation of Aquila. It is a type of evolved star known as an S-type star. Due to its relatively close distance of 1,200 light-years and equatorial location, it is easy to observe and heavily studied.

<span class="mw-page-title-main">RT Virginis</span> Star in the constellation Virgo

RT Virginis is a variable star in the equatorial constellation of Virgo, abbreviated RT Vir. It ranges in brightness from an apparent visual magnitude of 7.7 down to 9.7, which is too faint to be visible to the naked eye. Based on parallax measurements made with the VLBI, the distance to this star is approximately 740 light years. It is receding from the Sun with a radial velocity of 17 km/s.

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

RS Cancri, also known as HR 3639 and HD 78712, is a star about 490 light years from the Earth in the constellation Cancer. It is a semiregular variable star, ranging in brightness from magnitude 5.4 to 7.3 over a period of about 229 days. During the time intervals when it is brighter than magnitude 6, it may be faintly visible to the naked eye of an observer far from city lights.

References

  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. 1 2 3 4 5 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. 1 2 3 4 "EP Aqr". The International Variable Star Index. AAVSO. Retrieved 29 May 2022.
  4. 1 2 3 4 5 6 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. 1 2 3 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. 1 2 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. 1 2 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. 1 2 3 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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