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]

In 1877, John Birmingham published a set of ten magnitude estimates for EP Aquarii (number 596 on his list) made during the 1870s, which ranged from magnitude 6 to 8. He listed the star as "Variable (?)", although he also claimed to have observed "a quick change" in magnitude. [12] Birminghan's magnitude range is far wider than the 6.37 to 6.82 range listed in the GCVS, [13] nonetheless Birmingham's publication was cited as the reference when EQ Aquarii received its variable star designation in 1973. [14]

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. [15] 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. [16] [17] 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. [18] [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. [19] 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.

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">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.

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.

44 Aquarii is a single star located 336 light years away from the Sun in the equatorial constellation of Aquarius. 44 Aquarii is its Flamsteed designation. It is visible to the naked eye as a dim, yellow-hued star with an apparent visual magnitude of 5.75. This body is moving away from the Earth with a heliocentric radial velocity of +7.4 km/s.

<span class="mw-page-title-main">74 Aquarii</span> Triple star system in the constellation Aquarius

74 Aquarii is a triple star system in the constellation of Aquarius. 74 Aquarii is its Flamsteed designation and it also bears the variable star designation HI Aquarii. The combined apparent visual magnitude is 5.8, although it is very slightly variable, and it is located at a distance of 590 light-years from Earth.

17 Aquarii, abbreviated 17 Aqr, is a spectroscopic binary star system in the constellation of Aquarius. 17 Aquarii is the Flamsteed designation. It appears to the naked eye as a faint sixth magnitude star, having a combined apparent visual magnitude of 5.99. The distance to 17 Aqr can be estimated from its annual parallax shift of 4.9 mas, which yields a separation of around 660 light years. It is moving further away with a heliocentric radial velocity of 18 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">70 Aquarii</span> Star in the constellation Aquarius

70 Aquarii is a variable star located 425 light years away from the Sun in the equatorial constellation of Aquarius. It has the variable star designation FM Aquarii; 70 Aquarii is the Flamsteed designation. It is near the lower limit of visibility to the naked eye, appearing as a dim, yellow-white hued star with a baseline apparent visual magnitude of 6.19. This star is moving closer to the Earth with a heliocentric radial velocity of –5.8 km/s.

<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">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">LP Aquarii</span> Star in the constellation Aquarius

LP Aquarii is a pulsating variable star in the constellation of Aquarius that varies between magnitudes 6.30 and 6.64. The position of the star near the ecliptic means it is subject to lunar occultations.

<span class="mw-page-title-main">14 Aquarii</span> Star in the constellation Aquarius

14 Aquarii is red giant star. 14 Aquarii is the Flamsteed designation; it also bears the variable star designation IW Aquarii. It is a semiregular variable with an amplitude of a tenth of a magnitude, and shows variations on a timescale of just one day. At its brightest, magnitude 6.44, it could be faintly visible to the naked eye under ideal observing conditions.

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

W Andromedae is a variable star in the constellation of Andromeda. It is classified as a Mira variable and S-type star, and varies from an apparent visual magnitude of 14.6 at minimum brightness to a magnitude of 6.7 at maximum brightness, with a period of approximately 397.3 days.

67 Aquarii is a star located 484 light years away from the Sun in the zodiac constellation of Aquarius. 67 Aquarii is its Flamsteed designation. It is a dim, blue-white hued star near the lower limit of visibility to the naked eye with an apparent visual magnitude of 6.40. At the distance of this star, its visual magnitude is diminished by an extinction of 0.11 due to interstellar dust. The position of this star near the ecliptic means it is subject to lunar eclipses.

<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 1,530 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">IK Tauri</span> Mira variable star in the constellation Taurus

IK Tauri or NML Tauri is a Mira variable star located about 280 parsecs (910 ly) from the Sun in the zodiac constellation of Taurus.

<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. ↑ Birmingham, J. (1877). "The Red Stars: Observations and Catalogue". The Transactions of the Royal Irish Academy. 26: 249–354. Bibcode:1877TRIA...26..249B. JSTOR   30079086 . Retrieved 18 November 2024.
  13. ↑ Samus, N. N.; Goranskij, V. P.; Durlevich, O. V.; Kazarovets, E. V.; Kireeva, N. N.; Pastukhova, E. N.; Zharova, A. V. "General Catalogue of Variable Stars". Lomonosov Moscow State University. Retrieved 18 November 2024.
  14. ↑ Kukarkin, B. V.; Kholopov, P. N.; Kukarkina, N. P.; Perova, N. B. (October 1973). "59th Name-List of Variable Stars" (PDF). Information Bulletin on Variable Stars. 834: 1–22. Bibcode:1973IBVS..834....1K . Retrieved 18 November 2024.
  15. ↑ 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.
  16. ↑ 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.
  17. ↑ 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.
  18. ↑ 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.
  19. ↑ 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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