In the era of precision cosmology, it is essential to determine the Hubble constant empirically with an accuracy of one per cent or better
. At present, the uncertainty on this constant is dominated ...by the uncertainty in the calibration of the Cepheid period-luminosity relationship
(also known as the Leavitt law). The Large Magellanic Cloud has traditionally served as the best galaxy with which to calibrate Cepheid period-luminosity relations, and as a result has become the best anchor point for the cosmic distance scale
. Eclipsing binary systems composed of late-type stars offer the most precise and accurate way to measure the distance to the Large Magellanic Cloud. Currently the limit of the precision attainable with this technique is about two per cent, and is set by the precision of the existing calibrations of the surface brightness-colour relation
. Here we report a calibration of the surface brightness-colour relation with a precision of 0.8 per cent. We use this calibration to determine a geometrical distance to the Large Magellanic Cloud that is precise to 1 per cent based on 20 eclipsing binary systems. The final distance is 49.59 ± 0.09 (statistical) ± 0.54 (systematic) kiloparsecs.
All old Galactic globular clusters (GCs) studied in detail to date host at least two generations of stars, where the second is formed from gas polluted by processed material produced by massive stars ...of the first. We analyzed nine red giant branch stars belonging to the cluster Ruprecht 106. Targets were observed with the UVES VLT2 spectrograph. Spectra cover a wide range and allowed us to measure abundances for light (O, Na, Mg, Al), alpha (Si, Ca, Ti), iron-peak (Sc, V, Cr, Mn, Fe, Co, Ni, Cu, Zn), and neutron-capture (Y, Zr, Ba, La, Ce, Pr, Nd, Sm, Eu, Dy, Pb) elements. This result is supported also by an independent photometric test and by the horizontal branch morphology and the dynamical state. It is old (~12 Gyr) and, at odds with other GCs, has no alpha -enhancement. Clearly, its initial mass must have been significantly greater, but we have no current constraints on the amount of mass loss during its evolution.
In the era of precision cosmology, it is essential to determine the Hubble constant to an accuracy of three per cent or better. At present, its uncertainty is dominated by the uncertainty in the ...distance to the Large Magellanic Cloud (LMC), which, being our second-closest galaxy, serves as the best anchor point for the cosmic distance scale. Observations of eclipsing binaries offer a unique opportunity to measure stellar parameters and distances precisely and accurately. The eclipsing-binary method was previously applied to the LMC, but the accuracy of the distance results was lessened by the need to model the bright, early-type systems used in those studies. Here we report determinations of the distances to eight long-period, late-type eclipsing systems in the LMC, composed of cool, giant stars. For these systems, we can accurately measure both the linear and the angular sizes of their components and avoid the most important problems related to the hot, early-type systems. The LMC distance that we derive from these systems (49.97 ± 0.19 (statistical) ± 1.11 (systematic) kiloparsecs) is accurate to 2.2 per cent and provides a firm base for a 3-per-cent determination of the Hubble constant, with prospects for improvement to 2 per cent in the future.
omega Centauri is a peculiar globular cluster formed by a complex stellar population. To investigate it, we studied 172 stars belonging to the five SGBs that we can identify in our photometry, in ...order to measure their Fe/H content as well as estimate their age dispersion and the age-metallicity relation. The first important result is that all of these SGBs have a distribution in metallicity with a spread that exceeds the observational errors and typically displays several peaks that indicate the presence of several subpopulations. We were able to identify at least six of them based on their mean Fe/H content. These metallicity-based subpopulations are seen to varying extents in each of the five SGBs. Taking advantage of the age sensitivity of the SGB, we showed that, first of all, at least half of the subpopulations have an age spread of at least 2 Gyr. Then, we obtained an age-metallicity relation that is the most complete to date for this cluster. Interpretation of the age-metallicity relation is not straightforward, but it is possible that the cluster (or what we can call its progenitor) was initially composed of two populations with different metallicities. Because of their age, it is very unlikely that the most metal-rich derives from the most metal-poor by some kind of chemical evolution process, so they can be assumed to be two independent primordial objects, or perhaps two separate parts of a single larger object, that merged in the past to form the present-day cluster.
Abstract
Globular clusters (GCs) are natural laboratories where stellar and chemical evolution can be studied in detail. In addition, their chemical patterns and kinematics can tell us to which ...Galactic structure (disc, bulge, halo or extragalactic) the cluster belongs to. NGC 5927 is one of most metal-rich GCs in the Galaxy and its kinematics links it to the thick disc. We present abundance analysis based on high-resolution spectra of seven giant stars. The data were obtained using Fibre Large Array Multi Element Spectrograph/Ultraviolet Echelle Spectrograph (UVES) spectrograph mounted on ut2 telescope of the European Southern Observatory. The principal objective of this work is to perform a wide and detailed chemical abundance analysis of the cluster and look for possible Multiple Populations (MPs). We determined stellar parameters and measured 22 elements corresponding to light (Na, Al), alpha (O, Mg, Si, Ca, Ti), iron-peak (Sc, V, Cr, Mn, Fe, Co, Ni, Cu, Zn), and heavy elements (Y, Zr, Ba, Ce, Nd, Eu). We found a mean iron content of Fe/H = −0.47 ± 0.02 (error on the mean). We confirm the existence of MPs in this GC with an O–Na anti-correlation, and moderate spread in Al abundances. We estimate a mean α/Fe = 0.25 ± 0.08. Iron-peak elements show no significant spread. The Ba/Eu ratios indicate a predominant contribution from SNeII for the formation of the cluster.
Aims. We present abundance analysis based on high resolution spectra of 105 isolated red giant branch (RGB) stars in the Galactic Globular Cluster NGC 6121 (M 4). Our aim is to study its star ...population in the context of the multi-population phenomenon recently discovered to affect some Globular Clusters. Methods. The data have been collected with FLAMES+UVES, the multi-fiber high resolution facility at the ESO/VLT@UT2 telescope. Analysis was performed under LTE approximation for the following elements: O, Na, Mg, Al, Si, Ca, Ti, Cr, Fe, Ni, Ba, and NLTE corrections were applied to those (Na, Mg) strongly affected by departure from LTE. Spectroscopic data were coupled with high-precision wide-field UBVIC photometry from WFI@2.2 m telescope and infrared JHK photometry from 2MASS. Results. We derived an average Fe/H = -1.07±0.01 (internal error), and an α enhancement of ${\rm \alpha/Fe}$ = +0.39±0.05 dex (internal error). We confirm the presence of an extended Na-O anticorrelation, and find two distinct groups of stars with significantly different Na and O content. We find no evidence of a Mg-Al anticorrelation. By coupling our results with previous studies on the CN band strength, we find that the CN strong stars have higher Na and Al content and are more O depleted than the CN weak ones. The two groups of Na-rich, CN-strong and Na-poor, CN-weak stars populate two different regions along the RGB. The Na-rich group defines a narrow sequence on the red side of the RGB, while the Na-poor sample populate a bluer, more spread portion of the RGB. In the ${U}$ vs. $ {U-B}$ color magnitude diagram the RGB spread is present from the base of the RGB to the RGB-tip. Apparently, both spectroscopic and photometric results imply the presence of two stellar populations in M 4. We briefly discuss the possible origin of these populations.
NGC 3201 is a globular cluster (GC) which shows very peculiar kinematic characteristics including an extreme radial velocity and a highly retrograde orbit, strongly suggesting an extragalactic ...origin. Our aims are to study NGC 3201 in the context of multiple populations (MPs), hoping to constrain possible candidates for the self-enrichment by studying the chemical abundance pattern, as well as adding insight into the origin of this intriguing cluster. We present a detailed chemical abundance analysis of eight red giant branch stars using high-resolution spectroscopy. We measured 29 elements and found Fe/H = −1.53±0.01; we cannot rule out a metallicity spread of ∼0.12 dex, and an α-enhancement typical of halo GCs. However, significant spreads are observed in the abundances of all light elements except for Mg. We confirm the presence of an extended Na-O anticorrelation. n-capture elements generally are dominated by the r-process, in good agreement with the bulk of Galactic GCs. The total (C+N+O) abundance is slightly supersolar and requires a small downward correction to the isochrone age, yielding 11.4 Gyr. Kinematically, NGC 3201 appears likely to have had an extragalactic origin but its chemical evolution is similar to most other, presumably native, Galactic GCs.
Variability in NGC 3201 Giant Stars Cortés, C. C.; Llancaqueo Albornoz, Á.; Villanova, S. ...
The Astronomical journal,
09/2023, Letnik:
166, Številka:
3
Journal Article
Recenzirano
Odprti dostop
Abstract
We present the analysis of 510 light curves in
V
and
I
bands of 255 giant stars in the globular cluster NGC 3201. Our aim is to expand the sample of new types of variables reported in a ...previous study. These variables show a short period (
P
V
< 0.6 day) and a low amplitude (
A
(
V
) < 0.06 mag.). We first searched for variability using the generalized Lomb–Scargle and phase dispersion minimization periodograms of the sample, discarding 167 stars as non-variables. We then applied the significance test and reduced the sample to 88 giants, of which we classified 18 as possible variables, 11 as dubious, 41 as non-variables, and 18 as variables. We finally determined the cluster membership of this sample and grouped each star based on their light-curve shape. The discovered variables show periods in the range 0.2440 <
P
V
< 0.5868 days and amplitudes between 0.010 <
A
(
V
) < 0.064 mag. Within the sample of 18 variable stars, we report the discovery of an object with a period
P
V
= 0.3603 ± 0.0012 and amplitude
A
(
V
) = 0.703 ± 0.029 mag that shows a RR Lyrae ab-type light curve. Additionally, we report two RR Lyrae ab and c types with ultralow amplitude.
Abstract
In this paper we study stellar variability in the globular cluster NGC 3201 in the magnitude range
V
= 16–17, corresponding to the subgiant branch and blue stragglers region of the cluster. ...Our aim is to expand the sample of new type of variables with low amplitude and a short period found in previous papers. We used observations obtained at the Complejo Astronómico El Leoncito. We applied statistical tests and analyzed periodograms obtained by generalized Lomb–Scargle and phase dispersion minimization methods. We found five stars considered as variables and one as a possible variable. According to their periods (fluctuating between 0.33 and 0.57 days), amplitudes (between 0.03 and 0.87
V
magnitudes), the position in the color–magnitude diagram, and the shape of their phased light curves, they do not resemble any known variable star. Because stellar variability could be produced by more than one process, we propose to complement this work with a spectroscopic analysis to confirm our results.
Omega Centauri is no longer the only globular cluster known to contain multiple stellar populations, yet it remains the most puzzling. Due to the extreme way in which the multiple stellar population ...phenomenon manifests in this cluster, it has been suggested that it may be the remnant of a larger stellar system. In this work, we present a spectroscopic investigation of the stellar populations hosted in the globular cluster Delta *w Centauri to shed light on its still puzzling chemical enrichment history. With this aim, we used FLAMES+GIRAFFEatVLT to observe 300 stars distributed along the multimodal red giant branch of this cluster, sampling with good statistics the stellar populations of different metallicities. We determined chemical abundances for Fe, Na, O, and n-capture elements Ba and La. We confirm that Delta *w Centauri exhibits large star-to-star variations in iron with Fe/H ranging from ~--2.0 to ~--0.7 dex. Barium and lanthanum abundances of metal-poor stars are correlated with iron, up to Fe/H ~--1.5, while they are almost constant (or at least have only a moderate increase) in the more metal-rich populations. There is an extended Na-O anticorrelation for stars with Fe/H --1.3 while more metal-rich stars are almost all Na-rich. Sodium was found to mildly increase with iron over the entire metallicity range.
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