1,976 research outputs found
On the impact of Helium abundance on the Cepheid Period-Luminosity and Wesenheit relations and the Distance Ladder
This work analyses the effect of the Helium content on synthetic
Period-Luminosity Relations (PLRs) and Period-Wesenheit Relations (PWRs) of
Cepheids and the systematic uncertainties on the derived distances that a
hidden population of He-enhanced Cepheids may generate. We use new stellar and
pulsation models to build a homogeneous and consistent framework to derive the
Cepheid features. The Cepheid populations expected in synthetic color-magnitude
diagrams of young stellar systems (from 20 Myr to 250 Myr) are computed in
several photometric bands for Y = 0.25 and Y = 0.35, at a fixed metallicity (Z
= 0.008). The PLRs appear to be very similar in the two cases, with negligible
effects (few %) on distances, while PWRs differ somewhat, with systematic
uncertainties in deriving distances as high as about 7% at log P < 1.5.
Statistical effects due to the number of variables used to determine the
relations contribute to a distance systematic error of the order of few
percent, with values decreasing from optical to near-infrared bands. The
empirical PWRs derived from multi-wavelength datasets for the Large Magellanic
Cloud (LMC) is in a very good agreement with our theoretical PWRs obtained with
a standard He content, supporting the evidence that LMC Cepheids do not show
any He effect
Multipopulation aftereffects on the color-magnitude diagram and Cepheid variables of young stellar systems
Context: The evidence of a multipopulation scenario in Galactic globular
clusters raises several questions about the formation and evolution of the two
(or more) generations of stars. These populations show differences in their age
and chemical composition. These differences are found in old- and intermediate-
age stellar clusters in the Local Group. The observations of young stellar
systems are expected to present footprints of multiple stellar populations.
Aims: This theoretical work intends to be a specific step in exploring the
space of the observational indicators of multipopulations, without covering all
the combinations of parameters that may contribute to the formation of multiple
generations of stars in a cluster or in galaxy. The goal is to shed light on
the possible observational features expected by core He-burning stars that
belong to two stellar populations with different original He content and ages.
Methods: The tool adopted was the stellar population synthesis. We used new
stellar and pulsation models to construct a homogeneous and consistent
framework. Synthetic color-magnitude diagrams (CMDs) of young- and
intermediate-age stellar systems (from 20 Myr up to 1 Gyr) were computed in
several photometric bands to derive possible indicators of double populations
both in the observed CMDs and in the pulsation properties of the Cepheids.
Results: We predict that the morphology of the red/blue clump in VIK bands
can be used to photometrically indicate the two stellar populations in a rich
assembly of stars if there is a significant difference in their original He
content. Moreover, the period distribution of the Cepheids appears to be widely
affected by the coeval multiple generations of stars within stellar systems. We
show that the Wesenheit relations may be affected by the helium content of the
Cepheids.Comment: in press on A&
Photometric and spectroscopic study of the intermediate-age open cluster NGC 2355
In this paper we analyse the evolutionary status and properties of the old
open cluster NGC 2355, located in the Galactic anticentre direction, as a part
of the long term programme BOCCE. NGC 2355 was observed with LBC@LBT using the
Bessel , , and filters. The cluster parameters have been obtained
using the synthetic colour-magnitude diagram (CMD) method, as done in other
papers of this series. Additional spectroscopic observations with FIES@NOT of
three giant stars were used to determine the chemical properties of the
cluster. Our analysis shows that NGC 2355 has metallicity slightly less than
solar, with [Fe/H] dex, age between 0.8 and 1 Gyr, reddening
in the range 0.14 and 0.19 mag, and distance modulus of about 11 mag.
We also investigated the abundances of O, Na, Al, , iron-peak, and
neutron capture elements, showing that NGC 2355 falls within the abundance
distribution of similar clusters (same age and metallicity). The Galactocentric
distance of NGC~2355 places it at the border between two regimes of metallicity
distribution; this makes it an important cluster for the study of the chemical
properties and evolution of the disc.Comment: 20 pages, 11 figures, Accepted on MNRA
Tales from Dubna’s Oakwood: Bogoliubov, Pontecorvo, and the JINR Seminars
Not much has been said about the scientific milieu in which Bru- no Pontecorvo worked after his emigration to the USSR (1950): the Joint Institute for Nuclear Research (JINR) in Dubna. In this paper, we begin to fill this gap by focusing on some of the distinguished scientists he interacted with, besides direct collaborations, paying particular attention to Nikolai N. Bogoliubov around 1957
Large Binocular Telescope observations of PSR J2043+2740
We present the results of deep optical imaging of the radio/-ray
pulsar PSR J2043+2740, obtained with the Large Binocular Telescope (LBT). With
a characteristic age of 1.2 Myr, PSR J2043+2740 is one of the oldest (non
recycled) pulsars detected in -rays, although with still a quite high
rotational energy reservoir ( erg
s). The presumably close distance (a few hundred pc), suggested by the
hydrogen column density ( cm),
would make it a viable target for deep optical observations, never attempted
until now. We observed the pulsar with the Large Binocular Camera of the LBT.
The only object (V=25.440.05) detected within ~3" from the pulsar radio
coordinates is unrelated to it. PSR J2043+2740 is, thus, undetected down to
V~26.6 (3-), the deepest limit on its optical emission. We discuss the
implications of this result on the pulsar emission properties.Comment: 4 pages, 3 figures, accepted for publication on MNRA
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