# SR 12 (star)

SR 12 (also known as V2247 Oph) is a weak-line T-Tauri binary that has a planetary-mass companion with a detected accretion disk.

## The binary

SR 12 was discovered by Otto Struve and Mogens Rudkjøbing in 1949 as an emission-line star with a spectral type of M. The first letters of their names were used to name the star, together with the star number in their catalog. It was also observed as an x-ray source with the Einstein Observatory, having the designation ROX 21. The binary was discovered with the help of lunar occultations and speckle interferometry in 1987.
The binary is located in the ρ Ophiuchi star-forming region and is a weak-line T-Tauri binary, meaning it still accretes gaseous material from a circumstellar disk. There are differences in spectral type classifications of the individual stars. A K4/M2.5 binary was suggested, as well as a M3+M8 binary. The binary is separated by about 0.21 arcseconds, which corresponds to a separation of 24 AU. Speckle interferometry from SOAR does however find a lower separation of 0.1118 ±1.1 arcseconds.
The star is a variable with a rotation period that changes between 3.4 and 3.6 days. This is due to stellar spots at different latitudes corresponding to different rotation periods, which indicates photospheric shearing. The magnetic surface of the primary was mapped in 2010. The magnetic field showed changes within 1 week. Excess emissions concentrated at mid-latitude are seen as a footprint of an accretion funnel. The binary does not have any detection of circumbinary dust from Spitzer and ALMA observations.

## Planetary system

SR 12c was first detected in 2002 using the Infrared Survey Facility (IRSF), which was constructed and operated by Nagoya University and NAOJ and is located at the South African Astronomical Observatory. Follow-up observations were carried out with the Subaru Telescope in 2005 and 2008. Archival Hubble Space Telescope and Very Large Telescope (VLT) data were used to confirm the astrometry. The companion is also mentioned in a paper from 2002 that detects it in Hubble/NICMOS.
SR 12c has a separation of about 980 AU from the binary. The near-infrared spectrum suggested a spectral type of M9.0 ± 0.5 of the planetary-mass companion (PMC) and a mass of 14+7 −8 M$_J$. An additional higher-resolution near-infrared spectrum was taken in 2014, which showed signs of very low surface gravity, which is an indicator of youth. VLT spectroscopy resulted in a spectral type of L0 ± 1. A later work found that SR 12c is less massive with 11 ±3 M$_J$ and SED-fitting yielded a spectral type of L0 ±1. Several observations indicated that SR 12c is surrounded by a disk.
Observations with the VLT X-SHOOTER showed hydrogen emission lines, especially Hydrogen-alpha. This indicated that SR 12c accretes material at a rate of 10$^{−11.08±0.40}$ M$_☉$/year. The object also showed infrared excess from Spitzer IRAC photometry. Observations with ALMA did detect the disk, but was not able to resolve the disk, indicating a dust disk radius less than 5 AU and the radius might be about 0.3 AU if the continuum is optically thick. The disk has a dust mass twice as high as the disk around PDS 70c, but is less massive than OTS 44. Assuming the disk has only 1 mm grains, the dust mass of the disk is 0.012 M$_E$ (0.95 M$_L$). For a disk only made of 1 μm grains, it would have a dust mass of 0.054 M$_E$ (4.4 M$_L$). The disk also contains gas, as is indicated by the accretion of hydrogen, with the gas mass being on the order of 0.03 M$_J$ (about 9.5 M$_E$). ALMA did not detect any carbon monoxide in the disk.
The SR 12 planetary system :
| Companion (in order from star) | Mass | Semimajor axis (AU) | Orbital period (years) | Eccentricity | Inclination | Radius |
| c | 11 ±3 M$_J$ | 980 | — | — | — | 1.6 R$_J$ |

## Gallery

* Hubble image of SR 12 binary (upper right) and SR 12c (lower left). The orange part of the image shows H-alpha.
* The binary SR 12 with Hubble
* Wide view around SR 12 with VISTA, showing many young stars in the Ophiuchus dark clouds. SR 12 is the blue star at the center and SR 12c is the faint blue "star" below SR 12.