57,695 research outputs found
A photometric and spectroscopic survey of solar twin stars within 50 parsecs of the Sun: I. Atmospheric parameters and color similarity to the Sun
Solar twins and analogs are fundamental in the characterization of the Sun's
place in the context of stellar measurements, as they are in understanding how
typical the solar properties are in its neighborhood. They are also important
for representing sunlight observable in the night sky for diverse photometric
and spectroscopic tasks, besides being natural candidates for harboring
planetary systems similar to ours and possibly even life-bearing environments.
We report a photometric and spectroscopic survey of solar twin stars within 50
pc of the Sun. Hipparcos absolute magnitudes and (B-V)_Tycho colors were used
to define a 2 sigma box around the solar values, where 133 stars were
considered. Additional stars resembling the solar UBV colors in a broad sense,
plus stars present in the lists of Hardorp, were also selected. All objects
were ranked by a color-similarity index with respect to the Sun, defined by
uvby and BV photometry. Moderately high-resolution, high-S/N spectra were used
for a subsample of equatorial-southern stars to derive Teff, log g, and [Fe/H]
with average internal errors better than 50 K, 0.20 dex, and 0.08 dex,
respectively. Ages and masses were estimated from theoretical HR diagrams. The
color-similarity index proved very successful. We identify and rank new
excellent solar analogs, which are fit to represent the Sun in the night sky.
Some of them are faint enough to be of interest for moderately large
telescopes. We also identify two stars with near-UV spectra indistinguishable
from the Sun's. We present five new "probable" solar twin stars, besides five
new "possible" twins. Masses and ages for the best solar twin candidates lie
very close to the solar values, but chromospheric activity levels range
somewhat. We propose that the solar twins be emphasized in the ongoing searches
for extra-solar planets and SETI searches.Comment: 25 pages, 15 figures, 14 table
Maximum Entropy Inferences on the Axion Mass in Models with Axion-Neutrino Interaction
In this work we use the Maximum Entropy Principle (MEP) to infer the mass of
an axion which interacts to photons and neutrinos in an effective low energy
theory. The Shannon entropy function to be maximized is suitably defined in
terms of the axion branching ratios. We show that MEP strongly constrains the
axion mass taking into account the current experimental bounds on the neutrinos
masses. Assuming that the axion is massive enough to decay into all the three
neutrinos and that MEP fixes all the free parameters of the model, the inferred
axion mass is in the interval eV eV, which can be tested
by forthcoming experiments such as IAXO. However, even in the case where MEP
fixes just the axion mass and no other parameter, we found that eV eV in the DFSZ model with right-handed neutrinos. Moreover, a light
axion, allowed to decay to photons and the lightest neutrino only, is
determined by MEP as a viable dark matter candidate.Comment: 13 pages, 5 figures, typos corrected, figures update
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