# HD 15082

HD 15082
Observation data
Epoch J2000      Equinox J2000
Constellation Andromeda
Right ascension 02h 26m 51.0584s[1]
Declination +37° 33′ 01.736″[1]
8.3[2]
Characteristics
Spectral type kA5hA8mF4[3]
Variable type δ Sct[2]
Astrometry
Proper motion (μ) RA: −1.059±0.071 mas/yr
Dec.: −8.843±0.043 mas/yr
Parallax (π) 8.51 ± 0.24[1] mas
Distance 380 ± 10 ly
(118 ± 3 pc)
Details
Mass 1.55 ± 0.04[3] M
Surface gravity (log g) 4.3 ± 0.2[2] cgs
Temperature 7,400 ± 200[2] K
Metallicity [Fe/H] 0.1 ± 0.2[3] dex
Rotational velocity (v sin i) 86[2] km/s
Age 100[4] Myr
Other designations
BD+36 489, HD 15082, HIP 11397, SAO 55561, WASP-33.
Database references

HD 15082 (also known as WASP-33) is a star located roughly 380 light years away[1] in the northern constellation of Andromeda.[5] The star is a Delta Scuti variable and a planetary transit variable. A hot Jupiter type extrasolar planet, HD 15082b or WASP-33b, orbits this star with an orbital period of 1.22 days. It is the first Delta Scuti variable known to host a planet.[6]

## Spectrum

HD 15082 is an Am star, which makes its stellar classification challenging to discern. The hydrogen lines and effective temperature of the star are similar to spectral type A8, however the calcium II K line resembles that of an A5 star, and the metallic lines are more similar to an F4 star. The spectral type is thus written kA5hA8mF4.[3]

## Planet

The HD 15082 planetary system[3][7][note 1]
Companion
(in order from star)
Mass Semimajor axis
(AU)
Orbital period
(days)
b < 4.59 MJ 0.02558 (± 0.00023) 1.21987089 ± 1.5×10−07 0 87.67° 1.438 RJ

In 2010, the SuperWASP project announced the discovery of an extrasolar planet, designated HD 15082 b, orbiting the star. The discovery was made by detecting the transit of the planet as it passes in front of its star, an event which occurs every 1.22 days. As the planet crosses the star's disc, it causes the rotational broadening signature in the star's spectrum to change, enabling the determination of the sky-projected angle between the star's equator and the orbital plane of the planet to be determined. (This differs from the Rossiter–McLaughlin effect which is observed for radial velocity measurements). For HD 15082 b, this angle is about 250 degrees, indicating that it is in a retrograde orbit. Limits from radial velocity measurements imply it has less than 4.1 times the mass of Jupiter.[3] The exoplanet orbits so close to its star that its surface temperature is about 3,200 °C (5,790 °F).[8]

June 2015 NASA reported the exoplanet has a stratosphere, and the atmosphere contains titanium oxide which creates the stratosphere. Titanium oxide is one of only a few compounds that is a strong absorber of visible and ultraviolet radiation, which heats the atmosphere, and able to exist in a gas-state in a hot atmosphere.[9][10]

Atmosphere of WASP-33b was detected by monitoring light as the planet passed behind its star (top) - Higher temperatures result in the low stratosphere due to molecules absorbing radiation from the star (right) - Lower temperatures at higher altitudes would result if there were no stratosphere (left).[9]

### Non-Keplerian features of motion for HD 15082 b

In view of the high rotational speed of its parent star, the orbital motion of HD 15082 b may be affected in a measurable way by the huge oblateness of the star and effects of general relativity.

First, the distorted shape of the star makes its gravitational field deviate from the usual Newtonian inverse-square law. The same is true for the Sun, and part of the precession of the orbit of Mercury is due to this effect. However, it is estimated to be ${\displaystyle 9\times 10^{9}}$ greater for HD 15082b.[11]

Other effects will also be greater for HD 15082b. In particular, precession due to general relativistic frame-dragging should be ${\displaystyle 3\times 10^{5}}$ greater for HD 15082b than for Mercury, where it is so far too small to have been observed. It has been argued that the oblateness of HD 15082 could be measured at a percent accuracy from a 10-year analysis of the time variations of the planet's transits.[11] Effects due to the planet's oblateness are smaller by at least one order of magnitude, and they depend on the unknown angle between the planet’s equator and the orbital plane, perhaps making them undetectable. The effects of frame-dragging are slightly too small to be measured by such an experiment.

## Notes

1. ^ Parameters from the photometric + radial velocity solution in table 3 of Cameron et al. (2010). Different analysis methods result in slightly different parameters, see Cameron et al. (2010) for details.

## References

1. ^ a b c d Brown, A. G. A; et al. (2016). "Gaia Data Release 1. Summary of the astrometric, photometric, and survey properties". Astronomy and Astrophysics. 595. A2. arXiv:. Bibcode:2016A&A...595A...2G. doi:10.1051/0004-6361/201629512.Gaia Data Release 1 catalog entry
2. Herrero, E.; et al. (February 2011), "WASP-33: the first δ Scuti exoplanet host star", Astronomy and Astrophysics, 526: L10, arXiv:, Bibcode:2011A&A...526L..10H, doi:10.1051/0004-6361/201015875
3. Collier Cameron, A.; et al. (2010). "Line-profile tomography of exoplanet transits - II. A gas-giant planet transiting a rapidly rotating A5 star". Monthly Notices of the Royal Astronomical Society. 407: 507. arXiv:. Bibcode:2010MNRAS.407..507C. doi:10.1111/j.1365-2966.2010.16922.x.
4. ^ Moya, A.; et al. (November 2011), "High spatial resolution imaging of the star with a transiting planet WASP-33", Astronomy & Astrophysics, 535: A110, arXiv:, Bibcode:2011A&A...535A.110M, doi:10.1051/0004-6361/201116889
5. ^ "WASP-33 b". ETD - Exoplanet Transit Database. Retrieved 2010-04-28.
6. ^ "Discovery Of A Pulsating Star That Hosts A Giant Planet", Science Daily, January 19, 2011
7. ^ Zhang, Michael; et al. (2017). "Phase curves of WASP-33b and HD 149026b and a New Correlation Between Phase Curve Offset and Irradiation Temperature". arXiv: [astro-ph.EP].
8. ^ "Hottest planet is hotter than some stars". Retrieved 2015-06-12.
9. ^ a b "NASA's Hubble Telescope Detects 'Sunscreen' Layer on Distant Planet". Retrieved 2015-06-11.
10. ^ Haynes, Korey; Mandell, Avi M.; Madhusudhan, Nikku; Deming, Drake; Knutson, Heather (2015). "Spectroscopic Evidence for a Temperature Inversion in the Dayside Atmosphere of the Hot Jupiter WASP-33b". The Astrophysical Journal. 806 (2): 146. arXiv:. Bibcode:2015ApJ...806..146H. doi:10.1088/0004-637X/806/2/146.
11. ^ a b Iorio, Lorenzo (2010-07-25), "Classical and relativistic node precessional effects in WASP-33b and perspectives for detecting them", Astrophysics and Space Science, 331 (2): 485–496, arXiv:, Bibcode:2011Ap&SS.331..485I, doi:10.1007/s10509-010-0468-x