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Discovery Of A Planetary System Orbiting A Young A0V Star SDSS J001557.30+041504.01

17/04/2012

It is with great pleasure that I am able to report on the news of the discovery of a multiple-planet system orbiting the young A-star (official Harvard spectral classification A0V) HD1160†. As part of the Gemini NICI (Near Infrared Coronagraphic Imager) Planet-Finding campaign, Nielsen et al. (2012) have discovered two low-mass planetary companions to HD1160 (SDSS J001557.303+041504.018) at distances of approximately 80AU and 530AU*.

N.B.* 1AU (Astronomical Unit) is designated as the distance between our Sun and the Earth, specifically the semi-major axis of the elliptical path of the Earth around the Sun: 1AU is equal to 149,597,870,7000 metres.

N.B.† Please see: [http://www2.keck.hawaii.edu/inst/nirc/fc/HD_1160.jpg] for the W.M.Keck Observatory image of HD1160.

The Gemini NICI Planet-Finding campaign was fueled by the probability of finding new exoplanets. As it stands, there are 762 extrasolar planets discovered to date, most of them at small separations (<5 AU) from their parent stars (Butler et al. 2006; Marcy et al. 2008; Mayor et al. 2009). In addition, 1235 transiting planet candidates have been discovered by NASA’s Kepler Mission (Borucki et al. 2011), effectively tripling the plausible census of exoplanet candidates. In a 2012 study, each star of the 100 billion or so in our Milky Way galaxy is estimated to host on average approximately 1.6 planets (Cassan et al. 2011). Accordingly, at least 160 billion star-bound planets may exist in the Milky Way Galaxy alone.

The Gemini NICI Planet-Finding Campaign is a 3-year survey which begun in December 2008 targeting about 300 young, nearby stars to directly image extrasolar giant planets (Liu et al. 2010b). The goals of the Campaign are to detect new planets and to investigate the properties and formation mechanism of planets at ≥10 AU separations. Designed specifically to detect planets, the NICI instrument (Toomey & Ftaclas 2003; Chun et al. 2008) consists of an 85-element curvature adaptive optics system, a Lyot coronagraph, and two cameras that can image simultaneously for spectral difference imaging (SDI; Racine et al. 1999), observing through two moderate-band filters around the H-band methane feature seen in cool substellar objects (Burrows et al. 1997; Baraffe et al. 2003). NICI also uses angular differential imaging (ADI), which holds the telescope rotator fixed, allowing speckle noise to be separated from real companions (Liu 2004; Marois et al. 2006).

Nielsen et al. (2012) have added proposed mass estimates to the actual observational discoveries. Estimates for the two planets, designated as HD1160B and HD1160C are quoted as 33.0±12.0 and 190.0±65.0 respectively. This, as you may see, is widely erroneous. Hence, further studies on the HD1160 system will need to increase the accuracy of the mass estimations for the two planetary bodies. Supplemented to this is the mass of the host star itself, estimated to be ~2.2.  These results compound previously known sampling bias. Massive stars are easier to observe, for obvious reasons. Hence, most exoplanets are giant planets with extreme masses much greater than that of Jupiter. In fact, most planets found resemble Jupiter or Neptune quite closely in mass.

However, the extreme masses tentatively observed in the HD1160 system is an exciting glimpse into the possible world of high-mass exoplanet with masses greater that 30. However, caution must be raised since these observations rely on very tentative observational constraints.

Journal References:

  • Biller, B.A. (2010) The Gemini NICI Planet-Finding Campaign: Discovery Of A Close Substellar Companion To The Young Debris Disk Star PZ Tel. The Astrophysical Journal: Letters, 720 (1): pp.L.82-L87.
  • Nielsen, E.L. et al. (2012) The Gemini NICI Planet-Finding Campaign: Discovery Of A Multiple System Orbiting the Young A Star HD 1160. The Astrophysical Journal750 (1), Article I.D.: 53.
  • Thomas, S. et al. (2012) Gemini Planet Imager: From Integration & Test To Planning ObservationsAmerican Astronomical Society, AAS Meeting #219.
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