106 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
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
Pulsating stars in the VMC survey
The VISTA survey of the Magellanic Clouds system (VMC) began observations in
2009 and since then, it has collected multi-epoch data at Ks and in addition
multi-band data in Y and J for a wide range of stellar populations across the
Magellanic system. Among them are pulsating variable stars: Cepheids, RR Lyrae,
and asymptotic giant branch stars that represent useful tracers of the host
system geometry.Comment: 8 pages, 7 figures, proceeding contribution of invited presentation
at "Wide-field variability surveys: a 21st-century perspective", San Pedro de
Atacama (Chile
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
The VMC Survey. XXII. Hierarchical Star Formation in the 30 Doradus-N158-N159-N160 Star-forming Complex
We study the hierarchical stellar structures in a ∼1.5 deg2 area covering the 30 Doradus-N158-N159-N160 star-forming complex with the VISTA Survey of Magellanic Clouds. Based on the young upper main-sequence stars, we find that the surface densities cover a wide range of values, from log(pc2) ≲ -2.0 to log(pc2) ≳ 0.0. Their distributions are highly non-uniform, showing groups that frequently have subgroups inside. The sizes of the stellar groups do not exhibit characteristic values, and range continuously from several parsecs to more than 100 pc; the cumulative size distribution can be well described by a single power law, with the power-law index indicating a projected fractal dimension D2 = 1.6 ± 0.3. We suggest that the phenomena revealed here support a scenario of hierarchical star formation. Comparisons with other star-forming regions and galaxies are also discussed.Fil: Sun, Ning-Chen. Peking University; ChinaFil: Grijs, Richard De. Peking University; ChinaFil: Subramanian, Smitha. Peking University; ChinaFil: Cioni, Maria-Rosa L.. Universita Zu Berlin. Universita Postdam; AlemaniaFil: Rubele, Stefano. Università di Padova; ItaliaFil: Bekki, Kenji. University of Western Australia; AustraliaFil: Ivanov, Valentin D.. European Southern Observatory; ChileFil: Piatti, Andres Eduardo. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Conicet - Córdoba; Argentina. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba; ArgentinaFil: Ripepi, Vincenzo. Osservatorio Astronomico di Capodimonte; Itali
Updated theoretical Period-Age and Period-Age-Color relations for Galactic Classical Cepheids: an application to the Gaia DR2 sample
Updated evolutionary and pulsational model predictions are combined in order
to interpret the properties of Galactic Classical Cepheids in the Gaia Data
Release 2. In particular, the location of the instability strip boundaries and
the analytical relations connecting pulsation periods to the intrinsic stellar
parameters are combined with evolutionary tracks to derive reliable and
accurate period-age, and the first theoretical period-age-color relations in
the Gaia bands for a solar chemical abundance pattern (=, =).
The adopted theoretical framework takes into account possible variations in the
mass-luminosity relation for the core helium-burning stage as due to changes in
the core convective overshooting and/or mass loss efficiency, as well as the
impact on the instability strip boundaries due to different assumptions for
superadiabatic convection efficiency. The inferred period-age and
period-age-color relations are applied to a selected sample of both fundamental
and first overtone Gaia Cepheids, and individual ages for the various adopted
theoretical scenarios are derived. The retrieved age distributions confirm that
a variation in the efficiency of superadiabatic convection in the pulsational
model computations has a negligible effect, whereas a brighter Mass-Luminosity
relation, as produced by mild overshooting, rotation or mass loss, implies
significantly older age predictions. Moreover, older Cepheids are found at
larger Galactocentric distances, while first overtone Cepheids are found to be
systematically older than the fundamental ones. The comparison with independent
age distribution analysis in literature supports the predictive capability of
current theoretical framework.Comment: 14 pages, 11 figures, 8 tables, accepted for publication in MNRA
New insights into the use of Ultra Long Period Cepheids as cosmological standard candles
Ultra Long Period Cepheids (ULPs) are pulsating variable stars with a period
longer than 80d and have been hypothesized to be the extension of the Classical
Cepheids (CCs) at higher masses and luminosities. If confirmed as standard
candles, their intrinsic luminosities, 1 to 3 mag brighter than typical CCs,
would allow to reach the Hubble flow and, in turn, to determine the Hubble
constant, H_0, in one step, avoiding the uncertainties associated with the
calibration of primary and secondary indicators. To investigate the accuracy of
ULPs as cosmological standard candles, we first collect all the ULPs known in
the literature. The resulting sample includes 63 objects with a very large
metallicity spread with 12 + log([O/H]) ranging from 7.2 to 9.2 dex. The
analysis of their properties in the VI period-Wesenheit plane and in the
color-magnitude diagram (CMD) supports the hypothesis that the ULPs are the
extension of CCs at longer periods, higher masses and luminosities, even if,
additional accurate and homogeneous data and a devoted theoretical scenario are
needed to get firm conclusions. Finally, the three M31 ULPs, 8-0326, 8-1498 and
H42, are investigated in more detail. For 8-1498 and H42, we cannot confirm
their nature as ULPs, due to the inconsistency between their position in the
CMD and the measured periods. For 8-0326, the light curve model fitting
technique applied to the available time-series data allows us to constrain its
intrinsic stellar parameters, distance and reddening.Comment: MNRAS - Accepted 2020 November 19. Received 2020 November 19; in
original form 2020 July 15 - 9 pages and 8 figure
VARIABLE STARS AND STELLAR POPULATIONS IN ANDROMEDA XXV. III. A CENTRAL CLUSTER OR THE GALAXY NUCLEUS?
We present B and V time series photometry of Andromeda XXV, the third galaxy in our program on the Andromeda’s satellites, which we have imaged with the Large Binocular Cameras of the Large Binocular Telescope. The field of Andromeda XXV is found to contain 62 variable stars, for which we present light curves and characteristics of the light variation (period, amplitudes, variability type, mean magnitudes, etc.). The sample includes 57 RR Lyrae variables (46 fundamental-mode—RRab, and 11 first-overtone—RRc, pulsators), 3 anomalous Cepheids, 1 eclipsing binary system, and 1 unclassified variable. The average period of the RRab stars ( =0.60 σ = 0.04 days) and the period–amplitude diagram place Andromeda XXV in the class of the Oosterhoff-Intermediate objects. From the average luminosity of the RR Lyrae stars we derive for the galaxy a distance modulus of (m–M)0 = 24.63 ± 0.17 mag. The color–magnitude diagram reveals the presence in Andromeda XXV of a single, metal-poor ([Fe/H] = ‑1.8 dex) stellar population as old as ∼10–12 Gyr, traced by a conspicuous red giant branch and the large population of RR Lyrae stars. We discovered a spherically shaped high density of stars near the galaxy center. This structure appears to be at a distance consistent with Andromeda XXV and we suggest it could either be a star cluster or the nucleus of Andromeda XXV. We provide a summary and compare the number and characteristics of the pulsating stars in the M31 satellites analyzed so far for variability.
Based on data collected with the Large Binocular Cameras at the Large Binocular Telescope
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