Ultraviolet Observations of Two Possible FK Comae Stars
Abstract
The controversial and rare class of FK Comae stars may be examples of a brief stage of low-mass binary evolution: the point at which the two cores of a contact binary merge to form a single star. At present, there are four members of the class (although the appropriateness of FK Comae as a prototype has been questioned). Optical follow-up observations of the serendipitous X-ray detections contained in the Einstein Observatory Extended Medium Sensitivity Survey (EMSS) have revealed two new candidates for the FK Comae class. Ultraviolet observations of the known FK Comae stars show that their chromospheric and transition region line fluxes are relatively stronger than those of active binaries such as the RS CVn and W UMa types. Ultraviolet observations of the two candidates from the EMSS could help to verify their status as FK Comae stars. We propose to make two LWP (high- and low-resolution) and one low-resolution SWP observation of the brighter of the two candidates in order to measure its O I, Si II, C II, He II, C IV, N V, and Mg II emission line fluxes. In addition, we will use the high-resolution Mg II h & k line profiles to study the kinematics of the chromosphere and compare it to the kinematical information obtained from photospheric lines, as well as look for evidence of an excretion disk. This, in addition to one low-resolution LWP exposure of the fainter candidate, form a core proposal of 2 US1 shifts and 1 half US2 shift which is extremely feasible for the IUE to observe. We also ask for an additional US1 shift and US2 half shift as part of a supplemental proposal to obtain a high-resolution LWP exposure of the fainter candidate. We realize, based upon previous observations of other stars which may be similar in nature, that such an exposure (10 hours maximum) will probably be insufficient to meet the objectives listed above. However, since such reasoning precludes the chance to make an unusual discovery and since the potential for finding unusually strong chromospheric exists, we have decided to ask for the time. We will not be surprised if the supplemental proposal is not granted, but are confident in the merits of the core proposal.
- Publication:
-
IUE Proposal
- Pub Date:
- 1989
- Bibcode:
- 1989iue..prop.3429L