HD 77407 and GJ 577: Two new young stellar binaries

Abstract

Abstract. We present the first results from our search for close stellar and sub-stellar companions to young nearby stars on the northern sky. Our infrared imaging observations are obtained with the 3.5 m Calar Alto telescope and the AO system ALFA. With two epoch observations which were separated by about one year, we found two co-moving companion candidates, one close to HD 77407 and one close to GJ 577. For the companion candidate near GJ 577, we obtained an optical spectrum showing spectral type M 4.5; this candidate is a bound low-mass stellar companion confirmed by both proper motion and spectroscopy. We estimate the masses for HD 77407 B and GJ 577 B to be ∼0.3 to 0.5 M and ∼0.16 to 0.2 M , respectively. Compared to Siess et al. (2000) models, each of the two pairs appears co-eval with HD 77407 A, B being 10 to 40 Myrs and GJ 577 A, B being ≥100 Myrs old. We also took multi-epoch high-resolution spectra of HD 77407 to search for sub-stellar companions, but did not find any with 3 M Jup as upper mass (m sin i) limit (for up to 4 year orbits); however, we detected a long-term radial velocity trend in HD 77407 A, consistent with a ∼0.3 M companion at ∼50 AU separation, i.e. the one detected by the imaging. Hence, HD 77407 B is confirmed to be a bound companion to HD 77407 A. We also present limits for undetected, but detectable companions using a deep image of HD 77407 A and B, also observed with the Keck NIRC2 AO system; any brown dwarfs were detectable outside of 0.5 arcsec (17 AU at HD 77407), giant planets with masses from ∼6.5 to 12 M Jup were detectable at ≥1.5 arcsec.

Spectral Typing of Late-Type Stellar Companions to Young Stars From Low-Dispersion Near-Infrared Integral Field Unit Data

“…The best fit (via Equation (1)) for the companion's spectral type is M3V-M6V. This is later than the M0V-M3V derived by Mugrauer et al (2004), but that determination was done with only H-band photometry. Still, our results on HD 77407 B are the most uncertain of any of the stars in this paper.…”

“…It is a nearby star, with a distance of 30.1 pc (van Leeuwen 2007). The companion was first detected by Mugrauer et al (2004) via near-IR AO. They also measured its radial velocity over two years and show that the star exhibits a long-term radial velocity trend.…”

The Hercules-Lyra association revisited

“…The same object was detected by Luhman et al (2007) in 2006 June, so our 2002 image is a 2nd pre-discovery after 2MASS. Relative astrometry, based on the calibration published in Mugrauer et al (2004), is summarized in Table 2. We used the shortest possible DIT of 0.842 s and 49 integrations were averaged to one frame per jitter position.…”

“…The data were reduced in a standard way and calibrated using the calibration provided in Mugrauer et al (2004). We resolved the binary companion ∼11 to the southwest of HH Leo (Fig.…”

Multiplicity among Widely Separated Brown Dwarf Companions to Nearby Stars: Gliese 337CD

“…Six such systems are currently known: Gl 569Bab (Forrest et al 1988;Martín et al 2000), GJ 1001BC (Goldman et al 1999;Golimowski et al 2004b), Gl 577BC (Lowrance 2001;McCarthy et al 2001;Mugrauer et al 2004;Lowrance et al 2005), Gl 417BC (Kirkpatrick et al 2001a;Bouy et al 2003), HD 130948BC (Potter et al 2002;Goto et al 2002), and Ind BC (Scholz et al 2003;McCaughrean et al 2004). All six binaries have high mass ratios (q k 0:6) and are separated by at least 45 AU from their apparently single and more massive main-sequence primaries.…”