25 research outputs found
Low mass variable stars in the globular cluster NGC 6397
We have conducted a photometric survey of the globular cluster NGC 6397 in a
search for variable stars. We obtained ~11h of time-resolved photometric images
with one ne European Southern Observatory-Very Large Telescope using the FOcal
Reducer and low dispersion Spectrograph imager distributed over two consecutive
nights. We analyzed 8391 light curves of stars brighter than magnitude 23 with
the 465 nm-filter, and we identified 412 variable stars, reaching ~ 4.8 +- 0.2
per cent of variability with timescales between 0.004 and 2d, with amplitudes
variation greater than +- 0.2 mag.Comment: 9 figures, complementary dat
Probing Mass Segregation in NGC 6397
In this study, we present a detailed study of mass segregation in the
globular clister NGC 6397. First, we carry out a photometric analysis of
projected ESO-VLT data (between 1 and 10 arcmin from the cluster centre),
presenting the luminosity function corrected by completeness. The luminosity
function shows a higher density of bright stars near the central region of the
data, with respect to the outer region. We calculate a deprojected model
(covering the whole cluster) estimating a total number of stars of 193000 +-
19000. The shapes of the surface brightness and density-number profiles versus
the radial coordinate r (instead of the projected coordinate R) lead to a
decreasing luminosity for an average star, and thus of mass, up to 1 arcmin,
quantifying the mass segregation. The deprojected model does not show evidence
of mass segregation outside this region
New SX Phe variables in the globular cluster NGC 288
We report the discovery of two new variable stars in the metal-poor globular
cluster NGC 288, found by means of time-series CCD photometry. We classified
the new variables as SX Phoenicis due to their characteristic fundamental mode
periods (1.02 +- 0.01 and 0.69 +- 0.01 hours), and refine the period estimates
for other six known variables. SX Phe stars are known to follow a well-defined
Period-Luminosity (P-L) relation and, thus, can be used for determining
distances; they are more numerous than RR Lyraes in NGC~288. We obtain the P-L
relation for the fundamental mode M_V = (-2.59 +- 0.18) log P_0(d) + (-0.34 +-
0.24) and for the first-overtone mode M_V = (-2.59 +- 0.18) log P_1(d) + (0.50
+- 0.25). Multi-chromatic isochrone fits to our UBV color-magnitude diagrams,
based on the Dartmouth Stellar Evolution Database, provide = -1.3 +-
0.1, E(B-V) = 0.02 +- 0.01 and absolute distance modulus (m-M)0 = 14.72 +- 0.01
for NGC 288.Comment: 8 pages, 9 figures, 3 table
A threshold phenomenon for embeddings of into Orlicz spaces
We consider a sequence of positive smooth critical points of the
Adams-Moser-Trudinger embedding of into Orlicz spaces. We study its
concentration-compactness behavior and show that if the sequence is not
precompact, then the liminf of the -norms of the functions is greater
than or equal to a positive geometric constant.Comment: 14 Page