| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Hercules[1] |
| Right ascension | 16h 30m 29.61858s[2] |
| Declination | +38° 20′ 50.3090″[2] |
| Apparent magnitude (V) | 8.15[3] |
| Characteristics | |
| Spectral type | G0 IV[3] |
| Apparent magnitude (B) | 8.76[4] |
| B−Vcolor index | 0.611 |
| Astrometry | |
| Radial velocity (Rv) | −17.93±0.13[2] km/s |
| Proper motion (μ) | RA: −77.963mas/yr[2] Dec.: 52.682mas/yr[2] |
| Parallax (π) | 13.1203±0.0162 mas[2] |
| Distance | 248.6 ± 0.3 ly (76.22 ± 0.09 pc) |
| Absolute magnitude (MV) | 3.65±0.12[5] |
| Details | |
| Mass | 1.345±0.020[5] M☉ |
| Radius | 1.541+0.046 −0.042[5] R☉ |
| Luminosity | 3.03+0.20 −0.18[5] L☉ |
| Surface gravity (log g) | 4.189+0.020 −0.021[5] cgs |
| Temperature | 6,147±50[3] K |
| Metallicity[Fe/H] | 0.36±0.05[3] dex |
| Rotational velocity (v sin i) | 6.0±0.5[3] km/s |
| Age | 2.6+0.3 −0.2[5] Gyr |
| Other designations | |
| Ogma,BD+38°2787,HD 149026,HIP 80838,SAO 65349,TOI-2024,TIC 255930614,GSC 03063-01587[4] | |
| Database references | |
| SIMBAD | data |
| Exoplanet Archive | data |
HD 149026, also namedOgma/ˈɒɡmə/,[6] is ayellow subgiantstar approximately 249light-years from theSun in theconstellation ofHercules. Anexoplanet (designatedHD 149026 b, later namedSmertrios) orbits the star.
HD 149026 is the star's identifier in theHenry Draper Catalog.[4] Following its discovery in 2005 the planet was designated HD 149026 b.
In July 2014 theInternational Astronomical Union (IAU) launchedNameExoWorlds, a process for giving proper names to certain exoplanets and their host stars.[7] The process involved public nomination and voting for the new names.[8] In December 2015, the IAU announced the winning names were Ogma for this star and Smertrios for its planet.[9]
The winning names based on those submitted by the Club d'Astronomie de Toussaint ofFrance; namely 'Ogmios' and 'Smertrios'.Ogmios was aGallo-Roman deity andSmertrios was aGallic deity of war. The IAU substituted the name ofOgma, a deity of eloquence, writing, and great physical strength in theCeltic mythologies ofIreland andScotland, and who may be related to Ogmios, because 'Ogmios' is the name of an asteroid (189011 Ogmios).[10]
In 2016, the IAU organized aWorking Group on Star Names (WGSN)[11] to catalog and standardize proper names for stars. In its first bulletin of July 2016,[12] the WGSN explicitly recognized the names of exoplanets and their host stars approved by the Executive Committee Working Group Public Naming of Planets and Planetary Satellites, including the names of stars adopted during the 2015 NameExoWorlds campaign. This star is now so entered in the IAU Catalog of Star Names.[6]
The star is thought to be much more massive, larger and brighter than theSun. The higher mass means that despite its considerably younger age (2.0Ga) it is already much moreevolved than the Sun. The internalfusion ofhydrogen in the core of the star is coming to an end, and it is beginning to evolve towardsred gianthood. At a distance of 249light-years,[2] the star is not visible to the unaided eye. However, it should be easily seen inbinoculars or a smalltelescope.[3]
The star is over twice as enriched withchemical elements heavier thanhydrogen andhelium as the Sun. Because of this and the fact that the star is relatively bright, a group ofastronomers inN2K Consortium began to study the star. The star's anomalous composition as measured may be surface pollution only, from the intake of heavy-element planetesimals.[13]
In 2005 an unusualextrasolar planet was discovered to be orbiting the star. DesignatedHD 149026 b, it was detectedtransiting the star allowing its diameter to be measured. It was found to be smaller than other transiting planets known at the time, meaning it is unusually dense for a closely orbitinggiant planet.[3] In 2007, the temperature of the giant planet was calculated to be 2,300 K (2,030 °C; 3,680 °F), generating so muchinfrared heat that it glows. It was proposed that the planet absorbs nearly all the sunlight and radiates it into space as heat.[14] Subsequent studies have not confirmed this, with a 2018 study finding the planet to be highly reflective (with aBond albedo of 0.53), along with a lower temperature.[15]
| Companion (in order from star) | Mass | Semimajor axis (AU) | Orbital period (days) | Eccentricity | Inclination | Radius |
|---|---|---|---|---|---|---|
| b (Smertrios) | 0.324±0.011 MJ | 0.04364±0.00022 | 2.87588874(59)[15] | 0.0028+0.019 −0.0024 | 84.50+0.60 −0.52° | 0.811+0.029 −0.027 RJ |
