WASP-44

WASP-44 is a G-type star about 1,180 light-years (360 parsecs) away in the constellation Cetus that is orbited by the Jupiter-size planet WASP-44b. The star is slightly less massive and slightly smaller than the Sun; it is also slightly cooler, but is more metal-rich. The star was observed by SuperWASP, an organization searching for exoplanets, starting in 2009; manual follow-up observations using WASP-44's spectrum and measurements of its radial velocity led to the discovery of the transiting planet WASP-44b. The planet and its star were presented along with WASP-45b and WASP-46b on May 17, 2011 by a team of scientists testing the idea that hot Jupiters tend to have circular orbits, an assumption that is made when the orbital eccentricity of such planets are not well-constrained.^[3]

WASP-44

Observation data Epoch J2000      Equinox J2000
Constellation	Cetus
Right ascension	00h 15m 36.76947s[1]
Declination	−11° 56′ 17.2848″[1]
Apparent magnitude (V)	13.05[2]
Characteristics
Spectral type	G8V[3]
Astrometry
Radial velocity (Rv)	−3.10±1.32[1] km/s
Proper motion (μ)	RA: 15.272(22) mas/yr[1] Dec.: −30.159(14) mas/yr[1]
Parallax (π)	2.7644±0.0199 mas[1]
Distance	1,180 ± 8 ly (362 ± 3 pc)
Details[4]
Mass	0.929+0.053 −0.050 M☉
Radius	0.923+0.021 −0.020 R☉
Luminosity	0.680+0.031 −0.029 L☉
Surface gravity (log g)	4.476±0.030 cgs
Temperature	5457±46 K
Metallicity [Fe/H]	0.099+0.092 −0.089 dex
Rotational velocity (v sin i)	3.20±0.90[5] km/s
Age	6.0+4.3 −3.8 Gyr
Other designations
TOI-259, TIC 12862099, WASP-44, GSC 05264-00740, 2MASS J00153675-1156172[2]
Database references
SIMBAD	data

Observational history

WASP-44 was observed between July and November 2009 by WASP-South, a station of the SuperWASP planet-searching program based at the South African Astronomical Observatory. Observations of the star revealed a periodic decrease in its brightness. WASP-South, along with the SuperWASP-North station at the Roque de los Muchachos Observatory on the Canary Islands, collected 15,755 photometric observations, allowing scientists to produce a more accurate light curve.^[3] Another set of observations yielded a 6,000 point photometric data set, but the light curve was prepared late and was not considered in the discovery paper.^[3]

The South African Astronomical Observatory, base of the WASP-South station, where WASP-44 was first observed

In 2010, a European science team investigated the star using the CORALIE spectrograph and collected seventeen spectra of WASP-44. From the spectra, radial velocity measurements were extrapolated. Analysis of collected CORALIE data ruled out the possibility that the detected radial velocity was caused by the blended spectrum of a spectroscopic binary star, supporting the possibility that the body orbiting WASP-44 was indeed a planet, designated WASP-44b.^[3]

The Leonhard Euler Telescope at La Silla Observatory in Chile was used to follow up on the planet circling WASP-44, searching for a point at which the planet transited, or crossed in front of, its host star. One transit was detected.^[3]

WASP-44, its recently discovered planet, the planets orbiting WASP-45 and WASP-46, and a discussion exploring the validity of the common assumption amongst scientists that closely orbiting hot Jupiter planets have highly circular orbits unless proven otherwise, were reported in a single discovery paper that was published on May 17, 2011 by the Royal Astronomical Society.^[3] The paper was submitted to the Monthly Notices of the Royal Astronomical Society on May 16, 2011.^[3]

Characteristics

WASP-44 is a G-type star (the same class of star as the Sun) that is located in the Cetus constellation. WASP-44 has a mass that is 0.951 times that of the Sun. In terms of size, WASP-44 has a radius that is 0.927 times that of the Sun. WASP-44 has an effective temperature of 5410 K (cooler than the Sun). However, the star is metal-rich with relation to the Sun. Its measured metallicity is [Fe/H] = 0.06, or 1.148 times that the amount of iron found in the Sun.^[6] WASP-44's chromosphere (outermost layer) is not active. The star also does not rotate at a high velocity.^[3]

The star has an apparent magnitude of 12.9. It cannot be seen from Earth with the naked eye.^[6]

Planetary system

There is one known planet in the orbit of WASP-44: WASP-44b. The planet is a hot Jupiter^[3] with a mass of 0.889 times that of Jupiter. Its radius is 1.14 times that of Jupiter. WASP-44b orbits its host star every 2.4238039 days at a distance of 0.03473 AU, approximately 3.47% the mean distance between the Earth and Sun.^[6] With an orbital inclination of 86.02º, WASP-44b has an orbit that exists almost edge-on to its host star with respect to Earth.^[6] WASP-44b's orbital eccentricity is fit to 0.036, indicating a mostly circular orbit.^[3] An analysis of transit timing variations to search for additional planets was negative.^[7]

The WASP-44 planetary system^[4]

Companion (in order from star)	Mass	Semimajor axis (AU)	Orbital period (days)	Eccentricity	Inclination	Radius
b	0.860+0.072 −0.068 MJ	0.03474+0.00040 −0.00043[5]	2.4238133(23)[5]	0.039+0.047 −0.028	85.98+0.39 −0.35°	1.127+0.035 −0.034 RJ