The Mass of the Cepheid Binary V636 Scorpii

Details The Mass of the Cepheid Binary V636 Scorpii The Mass of the Cepheid Binary V636 Scorpii

Oct 1998

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998apj...505..903b&link_type=abstract

The Astrophysical Journal, Volume 505, Issue 2, pp. 903-909.

Astronomy and Astrophysics

Astronomy

9

Stars: Binaries: Spectroscopic, Stars: Variables: Cepheids, Stars: Evolution, Stars: Individual: Constellation Name: V636 Scorpii

Scientific paper

The mass-luminosity relation for Cepheids depends on the degree of mixing in their main-sequence progenitors. Masses of Cepheids can be inferred by using different aspects of pulsation theory. These methods have in the past led to diverging results, showing that something was wrong in either evolution theory or pulsation theory or both. For some binary Cepheids dynamical masses, which are independent of pulsation and evolution theories, can be determined. V636 Sco is one of a handful of Cepheid binaries whose companions are bright enough in the ultraviolet that orbital radial velocities can be measured. We have here attempted to determine the radial velocity of the companion V636 Sco B to the Cepheid V636 Sco A by means of two Hubble Space Telescope (HST) spectra taken at phases of minimum and maximum Cepheid orbital velocities. The ratio of the orbital velocity of the companion and the Cepheid (which is the inverse of their mass ratio) came out to be 1.25 +/- 0.17. V636 Sco B has a spectral type B9.5 V, for which we expect a stellar mass of 2.5 M_&sun;. For the Cepheid we thus determine a mass of 3.1 +/- 0.4 M_&sun;, which is surprisingly low. If true, such a low mass would indicate an extremely large amount of excess mixing, which is very unlikely. We discuss the likely possibility that V636 Sco B may itself be a binary with an unseen secondary, in which case the mass derived from the two measurements discussed above is not correct. Although the error limits for the mass of each Cepheid are rather large, the combined mass-luminosity relation for all Cepheids studied by us so far by means of HST spectra indicates excess mixing corresponding to core convective overshoot by 0.25 to about 0.5 pressure scale height in the main-sequence progenitors of the Cepheids. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NASS-26555.

Affiliated with

Also associated with

No associations

Rating

The Mass of the Cepheid Binary V636 Scorpii does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.

If you have personal experience with The Mass of the Cepheid Binary V636 Scorpii, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and The Mass of the Cepheid Binary V636 Scorpii will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFWR-SCP-O-1720110