arXiv subjects

C. P. Deliyannis

Publications and source records attributed to C. P. Deliyannis.

21 records · Page 2Linked to original sources

arXiv1999

Astrometry with Hubble Space Telescope Fine Guidance Sensor 3: The Parallax of the Cataclysmic Variable RW Triangulum

RW Triangulum (RW Tri) is a 13th magnitude Nova-like Cataclysmic Variable star with an orbital period of 0.2319 days (5.56 hours). Infrared observations of RW Tri indicate that its secondary is most likely a late K-dwarf. Past analyses predicted a distance of 270 parsec, derived from a black-body fit to spectrum of the central part of the disk. Recently completed Hubble Space Telescope Fine Guidance Sensor interferometric observations allow us to determine the first trigonometric parallax to RW Tri. This determination puts the distance of RW Tri at 341, one of the most distant objects with a direct parallax measurement.

astro-ph↗

arXiv1998

Boron in the very metal-poor star BD-13 3442

The Goddard High Resolution Spectrograph (GHRS) of the Hubble Space Telescope (HST) has been used to observe the boron 2500 A region of BD-13 3442. At a metallicity of [Fe/H]=-3.00, this is the most metal-poor star ever observed for B. Nearly 26 hours of exposure time resulted in a detection. Spectrum synthesis using the latest Kurucz model atmospheres yields an LTE boron abundance of log e(B)=0.01 +/- 0.20. This value is consistent with the linear relation of slope ~1.0 between log e(B[LTE]) and [Fe/H] found for 10 halo and disk stars by Duncan et al. 1997. Using the NLTE correction of Kiselman and Carlsson (1996), the NLTE boron abundance is log e(B)=0.93 +/- 0.20. This is also consistent with the NLTE relation determined by Duncan et al. (1997) where the slope of log e(B[NLTE]) vs. [Fe/H] is ~0.7. These data support a model in which most production of B and Be comes from the spallation of energetic C and O nuclei onto protons and He nuclei, probably in the vicinity of massive supernovae in star-forming regions, rather than the spallation of cosmic ray protons and alpha particles onto CNO nuclei in the general interstellar medium.

astro-ph↗

arXiv1994

Flare Production of $^6$Li in Population~II Stars

Motivated by the recent report of a $^6$Li detection in the atmosphere of HD~84937, we couple stellar evolution calculations with light isotope production via stellar flares. We find that as a consequence of their small convective envelope mass near the turn-off point, low-metallicity dwarfs and subgiants may possess observable amounts of $^6$Li arising from such flare activity. We point out an observational test which could discriminate between flare produced $^6$Li and protostellar $^6$Li. In the $T_{\rm eff}$ range $6000-6600$~K, the $^7$Li/$^6$Li ratio on the subgiant branch should increase as a function of $T_{\rm eff}$ if flare production is important, whereas the same ratio should be constant if a protostellar origin is the source of the observed lithium. The absence of a flare produced variation in the $^7$Li/$^6$Li ratio would allow for a more reliable inference of the -- cosmologically important -- atmospheric depletion mechanisms in stars.

astro-ph↗