HD 18742

HD 18742 / Ayeyarwady
Location of HD 18742 (circled)
Observation data
Epoch J2000.0[1]      Equinox J2000.0[1]
Constellation Eridanus
Right ascension 03h 00m 10.65643s[1]
Declination −20° 48′ 09.3773″[1]
Apparent magnitude (V) 7.81[1]
Characteristics
Spectral type G8/K0IV[2]
B−V color index 0.93[1]
J−H color index 0.472[1]
J−K color index 0.623[1]
Astrometry
Radial velocity (Rv)−13.29[1] km/s
Proper motion (μ) RA: -19.599[1] mas/yr
Dec.: −22.666[1] mas/yr
Parallax (π)6.1858 ± 0.0248 mas[1]
Distance527 ± 2 ly
(161.7 ± 0.6 pc)
Details[3]
Mass1.36,[3] 1.73±0.19[4] M☉
Radius5.13 R☉
Luminosity13.18+5.44
−3.85,[5] 20.66±0.46[6] L☉
Surface gravity (log g)3.09 cgs
Temperature4940 K
Metallicity [Fe/H]-0.14[7] dex
Rotational velocity (v sin i)1.72±0.23[5], 2.98±0.50[8] km/s
Age2.49±0.58[5] Gyr
Other designations
BD−21° 533, CPD−21° 295, Gaia DR1 5079636964618154112, Gaia DR2 5079636934554540160, HD 18742, HIP 13993, SAO 168212, PPM 245676, TIC 71345433, TYC 5870-602-1, GSC 05870-00602, 2MASS J03001065-2048091[1]
Database references
SIMBADdata

HD 18742 (proper name Ayeyarwady) is a 8th-magnitude subgiant star located about 530 light-years (160 pc) away in the constellation of Eridanus. It is orbited by one confirmed exoplanet, super-Jupiter HD 18742 b (proper name Bagan), and possibly by another Jovian planetary candidate (HD 18742 c).

Stellar characteristics

HD 18742 is a yellow subgiant star with a spectral type of G8/K0 IV. Its precise physical parameters vary from publication to publication, with calculated radii ranging between 4.08–6.34 R☉,[5][9] and mass estimates falling mostly between 1.36–1.73 M☉, though a 2017 paper[7] suggests a significantly higher value of 2.58±0.24 M☉. The star has an effective temperature of about 5,000 K (4,730 °C; 8,540 °F) and a luminosity of 13.2[7] or 20.7[6] L☉, and is thought to be about 2.3–2.5 billion years old.[8][5] Seen from Earth, the star has an apparent magnitude of 7.81, making it visible with binoculars and by the naked eye under the darkest skies with effort.[10]

Nomenclature

In 2019, the Republic of the Union of Myanmar was assigned to giving the HD 18742 system a proper name as part of the IAU100 NameExoWorlds Project, planned to celebrate the hundredth anniversary of the International Astronomical Union (IAU), which grants the right to name an exoplanetary system to every state and territory in the world.[11] Names were submitted and selected within Myanmar, which were then presented to the IAU to be officially recognized.[12] On 17 December 2019, the IAU announced that HD 18742 and its confirmed planet, b, were named Ayeyarwady and Bagan, respectively.[13]

Ayeyarwady was named after a river of the same name, the longest and most important river in Myanmar. Bagan refers to one of the ancient cities of the country located right beside the Ayeyarwady, which was listed as a UNESCO World Heritage Site in 2019.[13]

Planetary system

In 2011, radial-velocity observations made at the W. M. Keck Observatory revealed the existence of one exoplanet around HD 18742.[8] The planet, HD 18742, is thought to be a gas giant with a minimum mass of 3.362 MJ, which orbits its host star at a distance of 1.82 AU once every 766 days (2.10 years).[3] Its orbit is nearly circular (i.e., with a low eccentricity), similar to planets in the Solar System.[14]

Other than the doppler shifts caused by HD 18742 b, radial-velocity measurements used to discover the planet also included an additional linear trend. Utilizing data gathered at the Keck Observatory between 2007 and 2015, Luhn et al. subtracted the effects of HD 18742 b from the radial-velocity curve, revealing a 900-day-period signal, possibly caused by another similar planet. Though the existence of such a planet would provide a far better match to the observed curve, this signal remains a planetary candidate since it would be in a 9:10 resonance with HD 18742 b, a non-physical resonance that is previously unheard of. Follow-up observations are expected to show the true nature of the system.[3]

The HD 18742 planetary system[3]
Companion
(in order from star) 		Mass Semimajor axis
(AU) 		Orbital period
(days) 		Eccentricity Inclination Radius
b (Bagan) ≥3.362 ± 1.236 MJ 1.82 766.419 ± 24.763 0.040 ± 0.035 — 1.166 RJ
c (unconfirmed) ≥2.426 ± 1.226 MJ 1.96 858.724 ± 40.797 0.056 ± 0.052 — 1.194 RJ

See also

References

  1. ^ a b c d e f g h i j k l "HD 18742". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 17 September 2024.
  2. ^ Houk, Nancy; Swift, Carrie (2000) [1999]. "Michigan catalogue of two-dimensional spectral types for the HD Stars ; vol. 5". VizieR Online Data Catalog. 5. Bibcode:1999MSS...C05....0H.
  3. ^ a b c d e Luhn, Jacob K.; Bastien, Fabienne A.; Wright, Jason T.; Johnson, John A.; Howard, Andrew W.; Isaacson, Howard (1 April 2019). "Retired A Stars and Their Companions. VIII. 15 New Planetary Signals around Subgiants and Transit Parameters for California Planet Search Planets with Subgiant Hosts". The Astronomical Journal. 157 (4): 149. arXiv:1811.03043. Bibcode:2019AJ....157..149L. doi:10.3847/1538-3881/aaf5d0. ISSN 0004-6256.
  4. ^ Mortier, A.; Santos, N. C.; Sousa, S. G.; Adibekyan, V. Zh.; Delgado Mena, E.; Tsantaki, M.; Israelian, G.; Mayor, M. (2013). "New and updated stellar parameters for 71 evolved planet hosts". Astronomy & Astrophysics. 557: A70. arXiv:1307.7870. Bibcode:2013A&A...557A..70M. doi:10.1051/0004-6361/201321641. ISSN 0004-6361.
  5. ^ a b c d e Jofré, E.; Petrucci, R.; Saffe, C.; Saker, L.; Artur de la Villarmois, E.; Chavero, C.; Gómez, M.; Mauas, P. J. D. (2015). "Stellar parameters and chemical abundances of 223 evolved stars with and without planets". Astronomy & Astrophysics. 574: A50. arXiv:1410.6422. Bibcode:2015A&A...574A..50J. doi:10.1051/0004-6361/201424474. ISSN 0004-6361.
  6. ^ a b 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. Gaia DR2 record for this source at VizieR.
  7. ^ a b c Stassun, Keivan G.; Collins, Karen A.; Gaudi, B. Scott (1 March 2017). "Accurate Empirical Radii and Masses of Planets and Their Host Stars with Gaia Parallaxes". The Astronomical Journal. 153 (3): 136. arXiv:1609.04389. Bibcode:2017AJ....153..136S. doi:10.3847/1538-3881/aa5df3. ISSN 0004-6256.
  8. ^ a b c Johnson, John Asher; Clanton, Christian; Howard, Andrew W.; Bowler, Brendan P.; Henry, Gregory W.; Marcy, Geoffrey W.; Crepp, Justin R.; Endl, Michael; Cochran, William D.; MacQueen, Phillip J.; Wright, Jason T.; Isaacson, Howard (1 December 2011). "Retired a Stars and Their Companions. Vii. 18 New Jovian Planets". The Astrophysical Journal Supplement Series. 197 (2): 26. arXiv:1108.4205. Bibcode:2011ApJS..197...26J. doi:10.1088/0067-0049/197/2/26. hdl:2152/42985. ISSN 0067-0049.
  9. ^ Stassun, Keivan G.; Oelkers, Ryan J.; Paegert, Martin; Torres, Guillermo; Pepper, Joshua; Lee, Nathan De; Collins, Kevin; Latham, David W.; Muirhead, Philip S.; Chittidi, Jay; Rojas-Ayala, Bárbara; Fleming, Scott W.; Rose, Mark E.; Tenenbaum, Peter; Ting, Eric B.; Kane, Stephen R.; Barclay, Thomas; Bean, Jacob L.; Brassuer, C. E.; Charbonneau, David; Ge, Jian; Lissauer, Jack J.; Mann, Andrew W.; McLean, Brian; Mullally, Susan; Narita, Norio; Plavchan, Peter; Ricker, George R.; Sasselov, Dimitar; Seager, S.; Sharma, Sanjib; Shiao, Bernie; Sozzetti, Alessandro; Stello, Dennis; Vanderspek, Roland; Wallace, Geoff; Winn, Joshua N. (9 September 2019). "The Revised TESS Input Catalog and Candidate Target List". The Astronomical Journal. 158 (4): 138. arXiv:1905.10694. Bibcode:2019AJ....158..138S. doi:10.3847/1538-3881/ab3467. ISSN 0004-6256.
  10. ^ Bortle, John E. (18 July 2006). "Gauging Light Pollution: The Bortle Dark-Sky Scale". Sky & Telescope. American Astronomical Society. Retrieved 17 September 2024.
  11. ^ "List of stars and planets". Name ExoWorlds. IAU. Retrieved 27 August 2019.
  12. ^ "Methodology". Name ExoWorlds. IAU. Retrieved 27 August 2019.
  13. ^ a b "Approved names". NameExoWorlds. IAU. Retrieved 24 December 2019.
  14. ^ Limbach, MA; Turner, EL (2015). "Exoplanet orbital eccentricity: multiplicity relation and the Solar System". Proc Natl Acad Sci U S A. 112 (1): 20–4. arXiv:1404.2552. Bibcode:2015PNAS..112...20L. doi:10.1073/pnas.1406545111. PMC 4291657. PMID 25512527.