Studies of multiple stellar systems -- IV. The triple-lined spectroscopic system Gliese 644

Abstract

We present a radial velocity study of the triple‐lined system Gliese 644 and derive spectroscopic elements for the inner and outer orbits with periods of 2.965 5 and 627 d. We also utilize old visual data, as well as modern speckle and adaptive optics observations, to derive a new astrometric solution for the outer orbit. These two orbits together allow us to derive masses for each of the three components in the system: MA=0.410±0.028 (6.9 per cent), MBa=0.336±0.016 (4.7 per cent), and MBb=0.304±0.014 (4.7 per cent) M⊙. We suggest that the relative inclination of the two orbits is very small. Our individual masses and spectroscopic light ratios for the three M stars in the Gliese 644 system provide three points for the mass–luminosity relation near the bottom of the main sequence, where the relation is poorly determined. These three points agree well with theoretical models for solar metallicity and an age of 5 Gyr. Our radial velocities for Gliese 643 and vB 8, two common proper motion companions of Gliese 644, support the interpretation that all five M stars are moving together in a physically bound group. We discuss possible scenarios for the formation and evolution of this configuration, such as the formation of all five stars in a sequence of fragmentation events leading directly to the hierarchical configuration now observed, versus formation in a small N cluster with subsequent dynamical evolution into the present hierarchical configuration.

The 0.4-$M_{\odot}$ eclipsing binary CU Cancri

“…The magnitude difference is about 1.4 mag in the V band and 0.35 mag in the K band. The apparent faintness of CU Cnc in the V band had already been pointed out by D99, Delfosse et al (2000) and Mazeh et al (2001). Note that the isochrones computed with the models of Baraffe et al (1998) and Siess et al (1997) plotted in the figure produce a reasonably close fit to the stars other than CU Cnc in both observational diagrams.…”

“…Even though CU Cnc is the only object with a mass around 0.4 M with fully characterised physical properties, there are other stars in this regime whose masses have been spectroscopically determined to good accuracy. This is the case of Gl 570C, Gl 623A, Gl 644A, Gl 644Ba, Gl 661A, and Gl 661B, all with masses between 0.34 and 0.42 M (see Forveille et al 1999;Ségransan et al 2000;Delfosse et al 2000;Martin et al 1998;Mazeh et al 2001). We have compiled V and K absolute magnitudes for these stars from Delfosse et al (2000).…”

Saturation Levels for White-Light Flares of Flare Stars: Variation of Minimum Flare Duration for Saturation

“…The flare energy, which is expressed by Equation (2) given by Gershberg (1972), has generally been used to examine the level of flare activity in many studies (see, e.g., Mazeh et al 2001;Lacy et al 1976;Walker 1981;Gershberg & Shakhovskaya 1983;Pettersen et al 1984;Mavridis & Avgoloupis 1986). The luminosity parameter L occurs in the expression of the energy E, as in all these and other studies.…”

“…The flare stars whose flare parameters are compared in this study are quite young stars, except for V1054 Oph. The masses were derived for each component of Wolf 629ABab by Mazeh et al (2001), and were shown to be 0.41 M for Wolf 629A, 0.336 M for Wolf 629Ba, and 0.304 M for Wolf 629Bb. In addition, Mazeh et al (2001) demonstrated that the age of the system is about 5 Gyr.…”

Infrared Detection of Low‐Mass Secondaries in Spectroscopic Binaries

“…In this subsection we present the full double-lined orbital solutions for the three orbits, derived with our ORB code (Mazeh, Krymolowski, & Latham 1993 ;Mazeh et al 2001). To derive the double-lined solution, we assign di †erent uncertainties to the primary and secondary velocities of the di †erent measurements.…”