18 Aquilae

18 Aquilae

Location of 18 Aquilae (circled)
Observation data Epoch J2000      Equinox J2000
Constellation	Aquila
Right ascension	19^h 06^m 58.60289^s[1]
Declination	+11° 04′ 16.4173″[1]
Apparent magnitude (V)	5.072
Characteristics
Spectral type	B8 III[2]
U−B color index	−0.44[3]
B−V color index	−0.08[3]
Variable type	Eclipsing[4]
Astrometry
Radial velocity (Rv)	−18.6[5] km/s
Proper motion (μ)	RA: −0.89[1] mas/yr Dec.: −32.11[1] mas/yr
Parallax (π)	6.43 ± 0.79 mas[1]
Distance	approx. 510 ly (approx. 160 pc)
Orbit[6]
Primary	A
Companion	B
Period (P)	205.16 yr
Semi-major axis (a)	0.399″
Eccentricity (e)	0.23
Inclination (i)	134.3°
Orbit[6]
Primary	Aa
Companion	Ab
Period (P)	1.3023 d
Semi-amplitude (K1) (primary)	27.6 km/s
Details
Aa
Mass	5.6[6] M☉
Luminosity	4,875[7] L☉
Rotational velocity (v sin i)	50[2] km/s
Ab
Mass	0.38[6] M☉
Luminosity	12.7[7] L☉
B
Mass	3.49[6] M☉
Other designations
Y Aquilae, 18 Aql, BD+10 3787, FK5 3525, HD 178125, HIP 93867, HR 7248, SAO 104488[8]
Database references
SIMBAD	data

18 Aquilae (abbreviated 18 Aql) is a triple star^[9] system in the constellation of Aquila. 18 Aquilae is the Flamsteed designation; it also bears the variable star designation Y Aquilae. It has an apparent visual magnitude of 5.07, making it bright enough to be seen with the naked eye. The distance to this system can be estimated from the annual parallax shift of 6.43 mas, yielding a value of around 510 light-years (160 parsecs) away from Earth.

It took decades to determine whether or not 18 Aquilae is a variable star. It was used as a standard star in Benjamin Apthorp Gould's Uranometria Argentina, published in 1879. Gould marked the star with an asterisk, indicating that he thought it is a variable star.^[10] Gustav Müller and Paul Kempf noted Gould's opinion in their 1894 work Potsdamer Photometrische Durchmusterung, but stated that their numerous observations did not confirm that the star is variable.^[11] That same year, Seth Carlo Chandler reported that 18 Aquilae is a variable star. He stated the star showed an "unmistakable periodicity" and derived a period of 4.986 days - nearly 4 times larger than what the period is now known to be.^[12] Chandler gave the star the name Y Aquilae. In 1898, Edward Charles Pickering and Paul S. Yendell announced that their observations of the star "fail to show any evidence of variation".^[13] In 1966, Robert Arnold Breinhorst established that Y Aquilae is variable in his PhD thesis.^[14]

A light curve for Y Aquilae, plotted from TESS data^[15]

The inner pair of stars in this system form a spectroscopic binary with a combined magnitude of 5.44 and an orbital period of 1.302 days. The primary component is a giant star with a stellar classification of B8 III.^[2] Because the orbital plane is inclined near the line of sight, two form an eclipsing binary system. The eclipse of the primary component causes a 0.04 drop in magnitude, while the eclipse of the secondary results in a decrease of 0.03.^[16] At an angular separation of 0.310 arcseconds is the magnitude 6.39 tertiary component.^[9] This system has a high peculiar velocity of 29.7 ± 3.9 km/s relative to the neighboring stars.^[17]

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. Levato, H. (January 1975). "Rotational velocities and spectral types for a sample of binary systems". Astronomy and Astrophysics Supplement Series. 19: 91–99. Bibcode:1975A&AS...19...91L.
3. Osawa, K.; Hata, S. (1962). "Three-color photometry of B8-A2 stars (II)". Annals of the Tokyo Astronomical Observatory. 7: 209. Bibcode:1962AnTok...7..209O.
4. Samus, N. N.; Durlevich, O. V.; et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)". VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S. 1. Bibcode:2009yCat....102025S.
5. Wilson, Ralph Elmer (1953). "General catalogue of stellar radial velocities". Carnegie Institute Washington D.C. Publication. Carnegie Institution of Washington. Bibcode:1953GCRV..C......0W.
6. Tokovinin, Andrei (2018-03-01). "The Updated Multiple Star Catalog". The Astrophysical Journal Supplement Series. 235 (1): 6. arXiv:1712.04750. Bibcode:2018ApJS..235....6T. doi:10.3847/1538-4365/aaa1a5. ISSN 0067-0049. S2CID 119047709.
7. De Greve, J. P.; Vanbeveren, D. (1980). "Close Binary Systems Before and after Mass Transfer - a Comparison of Observations and Theory". Astrophysics and Space Science. 68 (2): 433. Bibcode:1980Ap&SS..68..433D. doi:10.1007/BF00639709. S2CID 123281741.
8. "18 Aql". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2012-07-25.
9. Eggleton, P. P.; Tokovinin, A. A. (September 2008). "A catalogue of multiplicity among bright stellar systems". Monthly Notices of the Royal Astronomical Society. 389 (2): 869–879. arXiv:0806.2878. Bibcode:2008MNRAS.389..869E. doi:10.1111/j.1365-2966.2008.13596.x. S2CID 14878976.
10. Gould, Benjamin Apthorp (1879). "Uranometria Argentina: Brightness and position of every fixed star, down to the seventh magnitude, within one hundred degrees of the South Pole; with atlas". Resultados del Observatorio Nacional Argentino. 1: I-387. Bibcode:1879RNAO....1....1G. Retrieved 24 November 2024.
11. Muller, G.; Kempf, P. (1894). "Number 31. Neunter Band. Photometrische Durchmusterung des Nordlichen Himmels, anthaltend alle sterne der B.D. bis zur Grosse 7.5. Theil I. Zone 0 degrees bis + 20 degrees declination". Publikationen des Astrophysikalischen Observatoriums zu Potsdam. 9: 1–501. Bibcode:1894POPot...9....1M. Retrieved 24 November 2024.
12. Chandler, S. C. (November 1894). "On a new variable of short period". Astronomical Journal. 14 (329): 135. Bibcode:1894AJ.....14..135C. doi:10.1086/102123. Retrieved 24 November 2024.
13. Pickering, E. C.; Yendell, P. S. (June 1898). "The supposedly variable star Y Aquilae". Astrophysical Journal. 8: 57–59. Bibcode:1898ApJ.....8...57P. doi:10.1086/140496. Retrieved 24 November 2024.
14. Breinhorst, Robert Arnold (1966). Der veränderliche Y Aquilae: lichtelektrische Dreifarbenphotometrie zur Untersuchg der System-Eigenschaften. University of Bonn. Bibcode:1966PhDT.......142B.
15. "MAST: Barbara A. Mikulski Archive for Space Telescopes". Space Telescope Science Institute. Retrieved 8 December 2021.
16. Malkov, O. Yu.; et al. (February 2006). "A catalogue of eclipsing variables". Astronomy and Astrophysics. 446 (2): 785–789. Bibcode:2006A&A...446..785M. doi:10.1051/0004-6361:20053137. hdl:10995/73280.
17. Tetzlaff, N.; Neuhäuser, R.; Hohle, M. M. (January 2011). "A catalogue of young runaway Hipparcos stars within 3 kpc from the Sun". Monthly Notices of the Royal Astronomical Society. 410 (1): 190–200. arXiv:1007.4883. Bibcode:2011MNRAS.410..190T. doi:10.1111/j.1365-2966.2010.17434.x. S2CID 118629873.

External links

• Image 18 Aquilae
• HR 7248