Eta Apodis

Eta Apodis, Latinized from η Apodis, is a star in the southern circumpolar constellation Apus. Based upon parallax measurements from the Hipparcos mission, it is approximately 141 light-years (43 parsecs) from Earth. With an apparent visual magnitude of +4.9,^[2] it can be viewed with the naked eye from the southern hemisphere.

η Apodis

Location of η Apodis (circled)
Observation data Epoch J2000      Equinox J2000
Constellation	Apus
Right ascension	14h 18m 13.89774s[1]
Declination	−81° 00′ 27.9300″[1]
Apparent magnitude (V)	+4.89[2]
Characteristics
Spectral type	A2MA7-F2[3] or A2(m) CrEu[4]
U−B color index	+0.11[5]
B−V color index	+0.25[5]
Astrometry
Radial velocity (Rv)	−9.4[2] km/s
Proper motion (μ)	RA: −19.854 ± 0.227[6] mas/yr Dec.: −65.413 ± 0.222[6] mas/yr
Parallax (π)	23.1651 ± 0.1430 mas[6]
Distance	140.8 ± 0.9 ly (43.2 ± 0.3 pc)
Absolute magnitude (MV)	+1.76[7]
Details
Mass	1.77[8] M☉
Radius	2.13[8] R☉
Luminosity	15.5[8] L☉
Temperature	7,860 ± 20[8] K
Rotational velocity (v sin i)	17.2 ± 0.3[9] km/s
Age	250 ± 200[8] Myr
Other designations
CD−80 706, FK5 3129, HD 123998, HIP 69896, HR 5303, SAO 258693.[10]
Database references
SIMBAD	data

Properties

This star has about 1.77 times the mass of the Sun and 2.13 times the Sun's radius. It is radiating 15.5 times the luminosity of the Sun from its outer atmosphere at an effective temperature of 7,860 K.^[8] Eta Apodis is a young star with an age of about 250 million years.^[8]

The stellar classification of Eta Apodis shows this to be an Am star, which means the spectrum shows chemically peculiarities. In particular, it is an A2-type star showing an excess of the elements chromium and europium. The spectrum displays magnetically-induced features indicating an estimated surface field strength of roughly 360 G.^[4] Based upon observations with the Spitzer Space Telescope, this system is emitting an excess of 24 μm infrared radiation. This may be caused by a debris disk of dust orbiting at a distance of more than 31 astronomical units from the star.^[8]

In 2023, the star Eta Apodis made history as the first variable star discovery by a Maldivian team, the Space Cat Team, composed of astronomers Gabriel Cristian Neagu and Moosa Samaau. These astronomers harnessed data from the Transiting Exoplanet Survey Satellite (TESS) mission to establish Eta Apodis as an Alpha2 Canum Venaticorum-type variable star. This achievement stands as a noteworthy milestone in the realm of astronomy, underscoring the collaborative expertise of Maldivian astronomers. The star was included in the International Variable Star Index and also contains the internally given name SpaceCat-V1. ^[11]

Eta Apodis, with its intriguing features and newfound classification as a variable star, remains a focal point of scientific interest, prompting further astronomical investigations and explorations.

Naming

In Chinese caused by adaptation of the European southern hemisphere constellations into the Chinese system, 異雀 (Yì Què), meaning Exotic Bird, refers to an asterism consisting of η Apodis, ζ Apodis, ι Apodis, β Apodis, γ Apodis, δ¹ Apodis, α Apodis and ε Apodis. Consequently, η Apodis itself is known as 異雀七 (Yì Què qī, English: the Seventh Star of Exotic Bird.)^[12]

References

1. 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.
2. Wielen, R.; et al. (1999), "Sixth Catalogue of Fundamental Stars (FK6). Part I. Basic fundamental stars with direct solutions", Veroeffentlichungen des Astronomischen Rechen-Instituts Heidelberg, 35 (35), Astronomisches Rechen-Institut Heidelberg: 1, Bibcode:1999VeARI..35....1W
3. Houk, Nancy (1979), Michigan catalogue of two-dimensional spectral types for the HD stars, vol. 1, Ann Arbor, Michigan: Dept. of Astronomy, University of Michigan, Bibcode:1978mcts.book.....H
4. Bychkov, V. D.; Bychkova, L. V.; Madej, J. (August 2003), "Catalogue of averaged stellar effective magnetic fields. I. Chemically peculiar A and B type stars", Astronomy and Astrophysics, 407 (2): 631–642, arXiv:astro-ph/0307356, Bibcode:2003A&A...407..631B, doi:10.1051/0004-6361:20030741, S2CID 14184105
5. Johnson, H. L.; et al. (1966), "UBVRIJKL photometry of the bright stars", Communications of the Lunar and Planetary Laboratory, 4 (99): 99, Bibcode:1966CoLPL...4...99J
6. 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.
7. Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters, 38 (5): 331, arXiv:1108.4971, Bibcode:2012AstL...38..331A, doi:10.1134/S1063773712050015, S2CID 119257644.
8. Plavchan, Peter; et al. (June 2009), "New Debris Disks Around Young, Low-Mass Stars Discovered with the Spitzer Space Telescope", The Astrophysical Journal, 698 (2): 1068–1094, arXiv:0904.0819, Bibcode:2009ApJ...698.1068P, doi:10.1088/0004-637X/698/2/1068, S2CID 51417657
9. Díaz, C. G.; et al. (July 2011), "Accurate stellar rotational velocities using the Fourier transform of the cross correlation maximum", Astronomy & Astrophysics, 531: A143, arXiv:1012.4858, Bibcode:2011A&A...531A.143D, doi:10.1051/0004-6361/201016386, S2CID 119286673
10. "eta Aps -- Star", SIMBAD, Centre de Données astronomiques de Strasbourg, retrieved 2012-07-08.
11. "VSX : Detail for eta Aps". www.aavso.org. Retrieved 2023-10-16.
12. (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 7 月 29 日 Archived 2011-05-22 at the Wayback Machine