HD 18742#Planetary system
{{Short description|Star in the constellation Eridanus}}
{{use dmy dates|date=September 2024}}
{{Starbox begin|name=HD 18742 / Ayeyarwady}}
{{Starbox image
| image=
{{Location mark
|image=Eridanus IAU.svg|alt=|float=center|width=300
|label=|position=right
|mark=Red circle.svg|mark_width=8|mark_link=HD 18742
|x%=61|y%=36
}}
|caption=Location of HD 18742 (circled)
}}
{{Starbox observe
| constell = Eridanus
| dec = {{DEC|-20|48|09.3773}}
}}
{{Starbox character
| type =
}}
{{Starbox astrometry
| parallax = 6.1858
| p_error = 0.0248
| absmag_v =
}}
{{Starbox detail
| source = {{R|luhn19}}
| mass = 1.36,{{R|luhn19}} {{val|1.73|0.19}}{{R|Mortier2013}}
| radius = 5.13
| luminosity = {{val|13.18|5.44|3.85}},{{R|Jofre2015}} {{val|20.66|0.46}}
| gravity = 3.09
| metal_fe = −0.14{{R|Stassun2017}}
| temperature = 4940
| rotation =
| rotational_velocity = {{val|1.72|0.23}}{{R|Jofre2015}}, {{val|2.98|0.50}}{{R|johnson11}}
| age_gyr = {{val|2.49|0.58}}{{R|Jofre2015}}
}}
{{Starbox catalog
| names = {{odlist | BD=-21° 533 | CPD=-21° 295 | PPM=245676 | TYC=5870-602-1 | GSC=05870-00602 | Gaia DR2=5079636934554540160 | Gaia DR1=5079636964618154112 | 2MASS=J03001065-2048091 | HD=18742 | HIP=13993 | SAO=168212 | TIC=71345433}}
}}
{{Starbox reference
| Simbad = HD+18742
}}
{{Starbox end}}
HD 18742 (proper name Ayeyarwady) is a 8th-magnitude subgiant star located about {{convert|530|ly|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{{en dash}}6.34 {{Solar radius|link=y}},{{R|Jofre2015|Stassun2019}} and mass estimates falling mostly between 1.36{{en dash}}1.73 {{solar mass|link=y}}, though a 2017 paper{{R|Stassun2017}} suggests a significantly higher value of {{val|2.58|0.24}} {{solar mass}}. The star has an effective temperature of about {{convert|5000|K|C F}} and a luminosity of 13.2{{R|Stassun2017}} or 20.7{{R|DR2}} {{Solar luminosity|link=y}}, and is thought to be about 2.3{{en dash}}2.5 billion years old.{{R|johnson11|Jofre2015}} 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.
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. Names were submitted and selected within Myanmar, which were then presented to the IAU to be officially recognized. On 17 December 2019, the IAU announced that HD 18742 and its confirmed planet, b, were named Ayeyarwady and Bagan, respectively.
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.
Planetary system
In 2011, radial-velocity observations made at the W. M. Keck Observatory revealed the existence of one exoplanet around HD 18742.{{R|johnson11}} The planet, HD 18742, is thought to be a gas giant with a minimum mass of 3.362 {{Jupiter mass|link=y}}, which orbits its host star at a distance of 1.82 AU once every {{convert|766|day|year|abbr=off}}.{{R|luhn19}} Its orbit is nearly circular (i.e., with a low eccentricity), similar to planets in the Solar System.{{R|Limbach2015}}
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.{{R|luhn19}}
{{OrbitboxPlanet begin
}}
{{OrbitboxPlanet
| exoplanet = b (Bagan)
| mass = ≥3.362 ± 1.236
| period = 766.419 ± 24.763
| semimajor = 1.82
| eccentricity = 0.040 ± 0.035
| radius = 1.166
}}
{{OrbitboxPlanet hypothetical
| exoplanet = c
| mass = ≥2.426 ± 1.226
| period = 858.724 ± 40.797
| semimajor = 1.96
| eccentricity = 0.056 ± 0.052
| radius = 1.194
}}
{{Orbitbox end}}
See also
References
{{reflist|refs=
{{Cite web |title=Approved names |url=http://www.nameexoworlds.iau.org/final-results |access-date=2019-12-24 |website=NameExoWorlds |publisher=IAU}}
{{cite simbad |title=HD 18742 |access-date=2024-09-17}}
{{Cite Gaia DR2|5079636934554540160}}
{{cite magazine|magazine=Sky & Telescope|publisher=American Astronomical Society|title=Gauging Light Pollution: The Bortle Dark-Sky Scale|last=Bortle|first=John E.|date=18 July 2006|url=https://skyandtelescope.org/astronomy-resources/light-pollution-and-astronomy-the-bortle-dark-sky-scale/?c=y|access-date=2024-09-17}}
}}
External links
- {{cite encyclopedia|author=Jean Schneider|url=http://exoplanet.eu/catalog/hd_18742_b--894/|title=Planet HD 18742 b|encyclopedia=The Extrasolar Planet Encyclopaedia|access-date=2024-09-17}}
- {{Cite Exoplanet Archive|HD 18742|access-date=2024-07-30}}
- {{WikiSky|HD 18742}}
- {{cite web|url=http://www.nameexoworlds.iau.org/myanmar|title=Myanmar | IAU100 Name ExoWorlds|publisher=IAU|access-date=2024-09-17}}
Category:Eridanus (constellation)