1,213 research outputs found
Predicted properties of Galactic and Magellanic Classical Cepheids in the SDSS filters
We present the first extensive and detailed theoretical scenario for the
interpretation of Cepheid properties observed in the SDSS filters. Three sets
of nonlinear convective pulsation models, corresponding to the chemical
compositions of Cepheids in the Milky Way, the Large Magellanic Cloud and the
Small Magellanic Cloud respectively, are transformed into the SDSS bands by
relying on updated model atmospheres. The resulting observables, namely the
instability strip boundaries and the light curves, as well as the
Period-Luminosity, the Wesenheit and the Period-Luminosity-Colour relations,
are discussed as a function of the metal content, for both the fundamental and
the first overtone mode. The fundamental PL relations are found to deviate from
linear relations when computed over the whole observed Cepheid period range,
especially at the shorter wavelenghts, confirming previous findings in the
Johnson-Cousins bands. The obtained slopes are found to be mildly steeper than
the ones of the semiempirical and the empirical relations available in the
literature and covering roughly the same period range, with the discrepancy
ranging from about 13% in u-band to about 3% in z.Comment: Accepted for publication in MNRA
Cepheids and the Distance Ladder
Classical Cepheids plays a key role in the calibration of the extragalactic distance scale. In spite of their importance, some uncertainties related to their properties remain. In particular, a general consensus on the possible dependence on the metallicity of the host galaxy of the Cepheid properties has not been reached yet. These uncertainties could produce significant systematic errors in the calibration of the secondary distance indicators we need to reach cosmologically significant distances and in turn in the evaluation of the Hubble constant H 0. Possible solutions are discussed
On the Cepheid variables of nearby galaxies III. NGC 3109
We extended to the R and I bands the light curve coverage for 8 Cepheids
already studied in B and V by Capaccioli et al [AJ, 103, 1151 (1992)]. Sixteen
additional Cepheid candidates have been identified and preliminary periods are
proposed. The new Cepheids allow the period-luminosity relation to be extended
one magnitude fainter. Apparent B, V, R, and I distance moduli have been
calculated. Combining the data at different wavelengths, and assuming a true
distance modulus of 18.50 mag for the LMC, we obtain for NGC 3109 a true
distance modulus , corresponding to Mpc.
Adopting for the LMC, the interstellar reddening for the Cepheids
in NGC 3109 is consistent with 0. A discussion on the possible implications of
this result is presented. A comparison of the period-color, period-amplitude,
and period-luminosity relations suggests similar properties for the Cepheids in
the LMC, NGC 3109, Sextans A, Sextans B, and IC 1613, though the uncertainties
in the main parameter determination are still unsatisfactorily high for a firm
conclusion on the universality of the period-luminosity relation.Comment: 35 pages, aaspp4.sty, accepted for pubblication on Astron.
Pulsating stars as distance indicators and stellar population tracers
Pulsating stars can play a fundamental role as distance indicators to set the astronomical distance scale and to trace different stellar populations to infer information on the star formation history of the host galaxy. The most interesting variables are Classical Cepheids and RR Lyrae. A review of the properties of these variables and of the theoretical and observational approaches adopted in the literature are presented
Pulsational Evidence for Mass Loss in NGC 1866 Cepheids
Available observational data for the 20 known Cepheids in the LMC cluster NGC 1866 have been compared with Hubble Space Telescope observations, discovering in the cluster central region five additional variables, one of which appears to be a Cepheid candidate. We also reach the conclusion that only the photometric data for the seven variables in the cluster periphery appear accurate enough to allow a meaningful comparison with the results of pulsational theories. Out of these seven well-observed Cepheids, we find that the six probable cluster members are located in the color-magnitude diagram at the hot tip of the blue nose experienced by He-burning giants. Since evolutionary theory predicts for these giants an original mass on the order of 4 M⊙, we extend down to ~3 M⊙ the theoretical pulsational scenario already presented for M ≥ 5.0 M⊙. On this basis we discuss the four member Cepheids with VI magnitudes accurate enough to produce robust constraints on the pulsating structures. Among these variables, one finds evidence for a spread of masses by about 7%, with the structures following a tight mass-luminosity relation. Moreover, we show that periods and colors of the Cepheids give a robust indication of pulsator masses smaller than predicted by stellar evolution theory without mass loss, independently of the occurrence of core overshooting
Variable stars in the ultra-faint dwarf spheroidal galaxy Ursa Major I
We have performed the first study of the variable star population of Ursa
Major I (UMa I), an ultra-faint dwarf satellite recently discovered around the
Milky Way by the Sloan Digital Sky Survey. Combining time series observations
in the B and V bands from four different telescopes, we have identified seven
RR Lyrae stars in UMa I, of which five are fundamental-mode (RRab) and two are
first-overtone pulsators (RRc). Our V, B-V color-magnitude diagram of UMa I
reaches V~23 mag (at a signal-to-noise ratio of ~ 6) and shows features typical
of a single old stellar population. The mean pulsation period of the RRab stars
= 0.628, {\sigma} = 0.071 days (or = 0.599, {\sigma} = 0.032 days,
if V4, the longest period and brightest variable, is discarded) and the
position on the period-amplitude diagram suggest an Oosterhoff-intermediate
classification for the galaxy. The RR Lyrae stars trace the galaxy horizontal
branch at an average apparent magnitude of = 20.43 +/- 0.02 mag
(average on 6 stars and discarding V4), giving in turn a distance modulus for
UMa I of (m-M)0 = 19.94 +/- 0.13 mag, distance d= 97.3 +6.0/-5.7 kpc, in the
scale where the distance modulus of the Large Magellanic Cloud is 18.5 +/- 0.1
mag. Isodensity contours of UMa I red giants and horizontal branch stars
(including the RR Lyrae stars identified in this study) show that the galaxy
has an S-shaped structure, which is likely caused by the tidal interaction with
the Milky Way. Photometric metallicities were derived for six of the UMa I RR
Lyrae stars from the parameters of the Fourier decomposition of the V-band
light curves, leading to an average metal abundance of [Fe/H] = -2.29 dex
({\sigma} = 0.06 dex, average on 6 stars) on the Carretta et al. metallicity
scale.Comment: Accepted for publication in Ap
Dwarf spheroidal satellites of M31: I. Variable stars and stellar populations in Andromeda XIX
We present B,V time-series photometry of Andromeda XIX (And XIX), the most
extended (half-light radius of 6.2') of Andromeda's dwarf spheroidal
companions, that we observed with the Large Binocular Cameras at the Large
Binocular Telescope. We surveyed a 23'x 23' area centered on And XIX and
present the deepest color magnitude diagram (CMD) ever obtained for this
galaxy, reaching, at V~26.3 mag, about one magnitude below the horizontal
branch (HB). The CMD shows a prominent and slightly widened red giant branch,
along with a predominantly red HB, which, however, extends to the blue to
significantly populate the classical instability strip. We have identified 39
pulsating variable stars, of which 31 are of RR Lyrae type and 8 are Anomalous
Cepheids (ACs). Twelve of the RR Lyrae variables and 3 of the ACs are located
within And XIX's half light radius. The average period of the fundamental mode
RR Lyrae stars ( = 0.62 d, \sigma= 0.03 d) and the period-amplitude
diagram qualify And XIX as an Oosterhoff-Intermediate system. From the average
luminosity of the RR Lyrae stars ( = 25.34 mag, \sigma= 0.10 mag) we
determine a distance modulus of (m-M)= mag in a scale where
the distance to the Large Magellanic Cloud (LMC) is mag. The ACs
follow a well defined Period-Wesenheit (PW) relation that appears to be in very
good agreement with the PW relationship defined by the ACs in the LMC.Comment: accepted for publication in Ap
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