Tau1 Gruis

NASA

Tau1 Gruis is a yellow-orange star
somewhat brighter than our Sun,
Sol. (See a false-color Digitized
Sky Survey image of Tau1 Gruis
at NASA/JPL's "Planet Quest.")

System Summary

Tau1 Gruis is located around 109 light-years from Sol (HIPPARCOS Plx=30.04, e_Plx=0.73 mas), in the southcentral part (22:53:37.9-48:35:53.8, ICRS 2000.0) of Constellation Grus, the Crane -- south of Beta Gruis, southeast of Al Nair (Alpha Gruis), and northwest of Epsilon and Zeta Gruis. It may be visible from Earth for some Humans with the naked eye. According to the Yale Bright Star Catalogue, the star has three visual neighbors composed of an apparent wide binary around 152 ly away and a bluer star about 270 ly away: Tau2 Gruis or HD 216655 (G3-6 V) and HD 216656 (F7 V); and Tau3 or HR 8722 (Am). (Note - While Tau1 Gruis is not included in the Bright Star Map available on-line, it is available on the "150ly-h.zip" map file for the PC version of ChView that contains stars known to be located within 150 ly of Sol.) On September 17, 2002, astronomers announced the discovery of a Jupiter-type planet around this Sun-like star (press release, exoplanets.org, Anglo-Australian Observatory, and Jones et al, submitted 2002 -- details below). (See an animation of the planetary and potentially habitable zone orbits of the Tau1 Gruis system, with a table of basic orbital and physical characteristics.)

The Star

Tau1 Gruis is a yellow-orange dwarf star of possibly disputed spectral and luminosity type G0-3 V-IV (see: HR 8700 in the Yale Bright Star Catalogue versus the HIPPARCOS Catalogue.] It may have about 1.25 times Sol's mass (exoplanets.org), probably a larger diameter, and about 3.6 times its luminosity. Due to its unusually brightness, at least one source suspects that the star may be a highly evolved subgiant. Tau1 Gruis appears to be more than 1.4 times as enriched as Sol with elements heavier than hydrogen ("metallicity"), based on its abundance of iron (Favata, Micela, and Sciortino, 1997). The star's Ca-II H line suggests that Tau1 Gruis is chromospherically inactive (Jones et al, submitted 2002). Useful catalogue numbers and designations for this star include: Tau1 Gru, HR 8700, Hip 113044, HD 216435, CD-49 13988, CP(D)-49 11672, SAO 231343, Wo 9802, and LTT 9249.

"Planet b?"

© PPARC, David A. Hardy

Larger and jumbo images.

Planetary candidate "b" seen
with rings and two moons from
a third rocky moon, as imagined
by Hardy (more).

On September 17, 2002, a team of astronomers (including Hugh R. A. Jones, R. Paul Butler, Chris G. Tinney, Geoffrey W. Marcy, Alan J. Penny, Chris McCarthy, and Brad Carter) announced the discovery of a giant planet around this Sun-like star (press release, exoplanets.org, and Jones et al, submitted 2002). Radial velocity measurements suggest that Tau1 Gruis has a companion "b" with at least 1.23 times Jupiter's mass. It moves around Tau1 Gruis at an average distance of 2.6 AUs (a semi-major axis around the orbit distance of the center of the Main Asteroid Belt in the Solar System) in a relatively circular orbit (e=0.14 +/- 0.07) that takes about 1,326 +/- 300 days (or over 3.6 years) to complete (exoplanets.org; and Anglo-Australian Observatory). (See an animation of the planetary and potentially habitable zone orbits of the Tau1 Gruis system, with a table of basic orbital and physical characteristics.)

NASA

Cassini-Huygens Mission
to Saturn and Titan

Larger image.

Planet b is probably a gas giant
somewhat more massive than
Jupiter (shown here with Europa).

The orbit of an Earth-like planet (with liquid water) around Tau1 Gruis may be centered around 1.9 AUs -- between the orbital distance of Mars and the Main Asteroid Belt in the Solar System -- with an orbital period around 2.3 years. However, the orbit of planet b with an average distance of 2.6 AUs could have disrupted the development or later orbital stability of an Earth-type planet in Tau1 Gruis water zone. Astronomers would find it very difficult to detect an Earth-type planet in the water zone of this star using present methods.

Closest Neighbors

The following table includes all star systems known to be located within 10 light-years (ly), plus more bright stars within 10 to 20 ly, of Tau1 Gruis.

Star System	Spectra & Luminosity	Distance (light-years)
CD-45 14803	G3 V-IV	7.2
Zeta Gruis AB	G8-K0 V-III ?	9.2
CP-44 10252	K7 V	9.8
* plus bright stars *		. . .
CP-49 11603	G5 V	12
CD-55 9122	G5 V	13
Omicron Gruis 2?	F4 V	13
HR 8814 AB	F4-6 IV ?	14
Al Na'ir AB	B7 IV ?	16
CP-47 10013	G8 V	17
CP-41 9905	F5 V	18
CP-49 11653	F9 V	18
CP-54 10338	G5 V	18
CD-57 8761	G5 V	18

Other Information

Up-to-date technical summaries on these stars can be found at: Jean Schneider's Extrasolar Planets Encyclopaedia; the HIPPARCOS Catalogue using the VizieR Search Service mirrored from the Centre de Données astronomiques de Strasbourg (CDS); NASA's ADS Abstract Service for the Astrophysics Data System; and the SIMBAD Astronomical Database mirrored from CDS, which may require an account to access.

Grus, the Crane, is a small constellation of the Southern Hemisphere. Lying just below Piscis Austrinus (the Southern Fish), Grus was at one time part of that constellation. Grus was named by Johann Bayer and first listed in his 1603 star atlas, Uranometria. For more information about the stars and objects in this constellation and an illustration, go to Christine Kronberg's Grus. For an illustration, see David Haworth's Grus.

For more information about stars including spectral and luminosity class codes, go to ChView's webpage on The Stars of the Milky Way.