BD+56 2966 / HR 8832

BD+56 2966 designation comes from a catalogue that was originally published in 1863 by Friedrich Wilhelm August Argelander (1799-1875) on the position and brightness of 324,198 stars between +90° and -2° declination that were measured over 11 years from Bonn, Germany with his assistants Eduard Schönfeld (1828-1891) and Aldalbert Krüger (1832-1896). The catalogue became famous as the Bonner Durchmusterung ("Bonn Survey") and is typically abbreviated as BD. It was later expanded and extended during the early 20th Century with the Cordoba (observed from Argentina) then the Cape Photographic Durchmusterung (observed from South Africa).

As a relatively bright star in Earth's night sky, Star A is catalogued as Harvard Revised (HR) 8832, a numbering system derived from the 1908 Revised Harvard Photometry catalogue of stars visible to many Humans with the naked eye. The HR system has been preserved through its successor, the Yale Bright Star Catalogue -- updated and expanded through the hard work of E. Dorrit Hoffleit and others. HR 8832 is also listed as HD 219134 in the Henry Draper (1837-82) Catalogue with extension (HDE), a massive photographic stellar spectrum survey carried out by Annie Jump Cannon (1863-1941) and Edward Charles Pickering (1846-1919) from 1911 to 1915 under the sponsorship of a memorial fund created by Henry's wife, Anna Mary Palmer. (More discussion on star names and catalogue numbers is available from Alan MacRobert at Sky and Telescope and from Professor James B. Kaler's Star Names.)

The Star

BD+56 2966 is a orange-red main sequence dwarf star of spectral and luminosity type K3 V. This star has about 81 percent of Sol's mass (RECONS estimate), probably between 80 to 81 percent of its diameter (Pasinetti-Fracassini et al, 2001), and about 21 percent of its visual luminosity. According to one secondary reference which has not been verified, the star may be as enriched as Sol with elements heavier than hydrogen ("metallicity"), based on its abundance of iron. It is a New Suspected Variable star with the designation NSV 14458 and a Catalogue of Suspected Variable star as CSV 8833. Other useful star catalogue designations for BD+56 2966 include: HR 8832*, Gl 892, Hip 114622, HD 219134, SAO 35236, FK5 875, LHS 71, LTT 16826, and LFT 1767.

Hunt for Substellar Companions

Since BD+56 2966 the star is sort of like a distant cousin to Sol, some speculate whether it might just be bright enough to support Earth-type life on a planet lucky enough to orbit in its water zone. A search for faint companions using radial velocity analysis found no supporting evidence for Jupiter-sized sized object within three AUs and objects larger than three Jupiter-masses within six AUs (Cummings et al, 1999). On the other hand, the failure to find large substellar objects like brown dwarfs or a Jupiter- or Saturn-class planet in a "torch" orbit (closer than the Mercury to Sun distance) around BD+56 2966 -- with even the highly effective radial-velocity methods of Geoff Marcy and Paul Butler -- bodes well for the possibility of Earth-type terrestrial planets around this star.

Indeed, the distance from BD+56 2966 where an Earth-type planet would be "comfortable" with liquid water is centered around only 0.46 AU -- just beyond Mercury's orbital distance in the Solar System. At that distance from the star, such a planet would have an orbital period of about 125 days -- just over a third of an Earth year. Astronomers are hoping to use NASA's Terrestrial Planet Finder (TPF) and the ESA's Darwin planned groups of observatories to search for a rocky inner planet in the so-called "habitable zone" (HZ) around BD+56 2966. As currently planned, the TPF will include two complementary observatory groups: a visible-light coronagraph to launch around 2014; and a "formation-flying" infrared interferometer to launch before 2020, while Darwin will launch a flotilla of three mid-infrared telescopes and a fourth communications hub beginning in 2015.

Life Around a Flare Star

Many dim, red (M) and some orange-red (K) dwarf stars exhibit unusually violent flare activity for their size and brightness. These flare stars are actually common because red dwarfs make up more than half of all stars in our galaxy. Although flares do occur on the Sun every so often, the amount of energy released in a Solar flare is small compared to the total amount of energy that Sol produces. However, a flare the size of a solar flare occurring on a orange-red dwarf star (such as BD+56 2966) that normally has less than 21 percent of than Sol's luminosity would be more noticeable.

Arnold O. Benz, Institute of Astronomy, ETH Zurich

High resolution and jumbo images (Benz et al, 1998).

BD+56 2966 is a flare star, like UV Ceti (Luyten
726-8 B) shown flaring at left. UV Ceti is an extreme
example of a flare star that can boost its brightness by
five times in less than a minute, then fall somewhat slower
back down to normal luminosity within two or three
minutes before flaring suddenly again after several hours.

Flare stars erupt sporadically, with successive flares spaced anywhere from an hour to a few days apart. A flare only takes a few minutes to reach peak brightness, and more than one flare can occur at a time. Moreover, in addition to bursts of light and radio waves, flares on dim red dwarfs may emit up to 10,000 times as many X-rays as a comparably-sized Solar flare on our own Sun, and so flares would be lethal to Earth-type life on planets near the flare star. Hence, Earth-type life around flare stars may be less likely because their planets must be located very close to dim orange-red dwarfs to be warmed sufficiently by star light to have liquid water (about 0.46 AU for BD+56 2966), which makes flares even more dangerous around such stars. In any case, the light emitted by late orange-red dwarfs may be too red in color for Earth-type plant life to perform photosynthesis efficiently.