Search results for "Dwarf star"
showing 4 items of 4 documents
Is it possible to explore Peccei-Quinn axions from frequency dependence radiation dimming?
2011
Abstract We explore how the Peccei–Quinn (PQ) axion parameter space can be constrained by the frequency-dependence dimming of radiation from astrophysical objects. To do so we perform accurate calculations of photon–axion conversion in the presence of a variable magnetic field. We propose several tests where the PQ axion parameter space can be explored with current and future astronomical surveys: the observed spectra of isolated neutron stars, occultations of background objects by white dwarfs and neutron stars, the light-curves of eclipsing binaries containing a white dwarf. We find that the lack of dimming of the light-curve of a detached eclipsing white dwarf binary recently observed, l…
Observational Approach and Perspective
1983
Well you did not cover more than half of my planned talk! (laughter). Let me comment on interferometric techniques, in particular speckle imaging which you mentioned. Doing speckle imaging with the largest telescopes now available will not give you better than the theoretical resolving power of the telescope. With a 4m telescope that is about 30 marc sec in the visible. That happens to be the radius of the supergiant Betelguese. So you are not going to achieve much with speckle imaging on these stars. One technique which has not been adequately exploited is that of lunar occultation which can give much better angular resolution than speckle, of the order of 2-3 marc sec. By using suitably c…
Old MS stars in young moving groups
2009
The associations and moving groups of young stars are excellent laboratories to investigate the stellar formation in the solar neighborhood. Past results confirmed that a non-negligible fraction of old main-sequence stars is present in the lists of members of the young stellar kinematic groups. A detailed study on the properties of these samples is needed to separate the young stars from old main-sequence stars with similar space motion, in order to identify the origin of these structures. Our intention is to characterize the sample of stars members of the young moving groups and determine their age distribution to quantify the contamination by old main-sequence stars, in particular, in the…
Stellar parameters & abund. from BACCHUS analysis
2019
Data from the SDSS-IV/Apache Point Observatory Galactic Evolution Experiment (APOGEE-2) have been released as part of SDSS Data Releases 13 (DR13) and 14 (DR14). These include high-resolution H-band spectra, radial velocities, and derived stellar parameters and abundances. DR13, released in 2016 August, contained APOGEE data for roughly 150000 stars, and DR14, released in 2017 August, added about 110000 more. Stellar parameters and abundances have been derived with an automated pipeline, the APOGEE Stellar Parameter and Chemical Abundance Pipeline (ASPCAP). We evaluate the performance of this pipeline by comparing the derived stellar parameters and abundances to those inferred from optical …