  | |
| 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−Vcolor index | 0.93[1] |
| J−Hcolor index | 0.472[1] |
| J−Kcolor 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] |
| Distance | 527 ± 2 ly (161.7 ± 0.6 pc) |
| Details[3] | |
| Mass | 1.36,[3]1.73±0.19[4] M☉ |
| Radius | 5.13 R☉ |
| Luminosity | 13.18+5.44 −3.85,[5]20.66±0.46[6] L☉ |
| Surface gravity (log g) | 3.09 cgs |
| Temperature | 4940 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 |
| Age | 2.49±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 | |
| SIMBAD | data |
HD 18742 (proper nameAyeyarwady) is a 8th-magnitudesubgiant star located about 530 light-years (160 pc) away in theconstellation ofEridanus. It is orbited by one confirmedexoplanet,super-Jupiter HD 18742 b (proper name Bagan), and possibly by anotherJovian planetary candidate (HD 18742 c).
HD 18742 is a yellow subgiant star with aspectral type of G8/K0 IV. Its physical parameters vary from publication to publication, with calculated radii ranging between 4.08–6.34R☉,[5][9] and mass estimates falling mostly between 1.36–1.73M☉, though a 2017 paper[7] suggests a significantly higher value of2.58±0.24M☉. The star has aneffective temperature of about 5,000 K (4,730 °C; 8,540 °F) and aluminosity of 13.2[7] or 20.7[6]L☉, and is thought to be about 2.3–2.5billion years old.[8][5] Seen fromEarth, the star has anapparent magnitude of 7.81, making it visible withbinoculars and by the naked eye under the darkest skies with effort.[10]
In 2019, theRepublic 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 ariver 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 aUNESCO World Heritage Site in 2019.[13]
In 2011,radial-velocity observations made at theW. M. Keck Observatory revealed the existence of one exoplanet around HD 18742.[8] The planet, HD 18742, is thought to be agas giant with a minimum mass of 3.362MJ, 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 loweccentricity), similar to planets in theSolar System.[14]
Other than thedoppler 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 9:10resonance 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]
| 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 ± 1.226MJ | 1.96 | 858.724 ± 40.797 | 0.056 ± 0.052 | — | 1.194 RJ |