We present new colour–effective temperature (
T
eff
) transformations based on the photometry of the early third data release (EDR3) of the ESA/
Gaia
mission. These relations are calibrated on a ...sample of about 600 dwarf and giant stars for which
T
eff
has previously been determined with the infrared flux method from dereddened colours. The 1
σ
dispersion of the transformations is of 60–80 K for the pure
Gaia
colours (BP−RP)
0
, (BP−
G
)
0
, and (
G
−RP)
0
, improving to 40–60 K for colours including the 2MASS
K
s
-band, namely (BP−
K
s
)0
, (RP−
K
s
)
0
, and (G−
K
s
)
0
. We validate these relations in the most challenging case of dense stellar fields, where the
Gaia
EDR3 photometry could be less reliable, providing guidance for the safe use of
Gaia
colours in crowded environments. We compare the
T
eff
from the
Gaia
EDR3 colours with those obtained from standard (
V
−
K
s
)
0
colours for stars in three Galactic globular clusters of different metallicity, namely NGC 104, NGC 6752, and NGC 7099. The agreement between the two estimates of
T
eff
is excellent, with mean differences of between –50 and +50 K, depending on the colour, and with 1
σ
dispersions around the mean
T
eff
differences of 25–50 K for most of the colours and below 10 K for (BP−
K
s
)
0
and (
G
−
K
s
)
0
. This demonstrates that these colours are analogous to (
V
−
K
s
)
0
as
T
eff
indicators.
Globular clusters with Gaia Pancino, E; Bellazzini, M; Giuffrida, G ...
Monthly notices of the Royal Astronomical Society,
05/2017, Letnik:
467, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Abstract
The treatment of crowded fields in Gaia data will only be a reality in a few years from now. In particular, for globular clusters, only the end-of-mission data (public in 2022–2023) will ...have the necessary full crowding treatment and will reach sufficient quality for the faintest stars. As a consequence, the work on the deblending and decontamination pipelines is still ongoing. We describe the present status of the pipelines for different Gaia instruments, and we model the end-of-mission crowding errors on the basis of available information. We then apply the nominal post-launch Gaia performances, appropriately worsened by the estimated crowding errors, to a set of 18 simulated globular clusters with different concentration, distance and field contamination. We conclude that there will be 103–104 stars with astrometric performances virtually untouched by crowding (contaminated by <1 mmag) in the majority of clusters. The most limiting factor will be field crowding, not cluster crowding: the most contaminated clusters will only contain 10–100 clean stars. We also conclude that (i) the systemic proper motions and parallaxes will be determined to 1 per cent or better up to ≃15 kpc, and the nearby clusters will have radial velocities to a few km s−1; (ii) internal kinematics will be of unprecedented quality, cluster masses will be determined to ≃10 per cent up to 15 kpc and beyond, and it will be possible to identify differences of a few km s−1 or less in the kinematics (if any) of cluster sub-populations up to 10 kpc and beyond; (iii) the brightest stars (V ≃ 17 mag) will have space-quality, wide-field photometry (mmag errors), and all Gaia photometry will have 1–3 per cent errors on the absolute photometric calibration.
Abstract
We present the first results of the Multi-Instrument Kinematic Survey of Galactic Globular Clusters (GGCs), a project aimed at exploring the internal kinematics of a representative sample of ...GGCs from the radial velocity of individual stars, covering the entire radial extension of each system. This is achieved by exploiting the formidable combination of multi-object and integral field unit spectroscopic facilities of the ESO Very Large Telescope. As a first step, here we discuss the results obtained for 11 clusters from high and medium resolution spectra acquired through a combination of FLAMES and KMOS observations. We provide the first kinematical characterization of NGC 1261 and NGC 6496. In all the surveyed systems, the velocity dispersion profile declines at increasing radii, in agreement with the expectation from the King model that best fits the density/luminosity profile. In the majority of the surveyed systems, we find evidence of rotation within a few half-mass radii from the center. These results are in general overall agreement with the predictions of recent theoretical studies, suggesting that the detected signals could be the relic of significant internal rotation set at the epoch of the cluster’s formation.
We derived potassium abundances in red-giant-branch stars in the Galactic globular clusters NGC 104 (144 stars), NGC 6752 (134 stars), and NGC 6809 (151 stars) using high-resolution spectra collected ...with FLAMES at the ESO – Very Large Telescope. In the samples we consider, we do not find significant intrinsic spreads in K/Fe, which confirms the previous findings, but which is at variance with the cases of the massive clusters NGC 2419 and NGC 2808. Additionally, marginally significant K/Fe−O/Fe anti-correlations are found in NGC 104 and NGC 6809, and K/Fe−Na/Fe correlations are found in NGC 104 and NGC 6752. No evidence of K/Fe−Mg/Fe anti-correlation are found. The results of our analysis are consistent with a scenario in which the process leading to the multi-populations in globular clusters also implies enrichment in the K abundance, the amplitude of the associated K/Fe enhancement becoming measurable only in stars showing the most extreme effects of O and Mg depletion. Stars enhanced in K/Fe have so far only been found in clusters harbouring some Mg-poor stars, while the other globulars, without a Mg-poor sub-population, show small or null K/Fe spreads.
We present iron, magnesium, calcium, and titanium abundances for 235 stars in the central region of the Sagittarius dwarf spheroidal galaxy (within 9.0′ ≃ 70 pc from the centre) from ...medium-resolution Keck/Deep Imaging Multi-Object Spectrograph spectra. All the considered stars belong to the massive globular cluster M 54 or to the central nucleus of the galaxy (Sgr, N). In particular we provide abundances for 109 stars with Fe/H ≥−1.0, more than doubling the available sample of spectroscopic metallicity and α-elements abundance estimates for Sgr dSph stars in this metallicity regime. We find for the first time a metallicity gradient in the Sgr, N population, whose peak iron abundance goes from Fe/H =−0.38 for R ≤ 2.5′ to Fe/H =−0.57 for 5.0 <R ≤ 9.0′. On the other hand, the trends of Mg/Fe, Ca/Fe, and Ti/Fe with Fe/H are the same over the entire region explored by our study. We reproduce the observed chemical patterns of the Sagittarius dwarf spheroidal as a whole with a chemical evolution model which implies that a high mass progenitor (MDM = 6 × 1010M⊙) and a significant event of mass-stripping occurred a few Gyr ago, presumably starting at the first peri-Galactic passage after infall.
Several recent studies have reported the detection of an anomalous color spread along the red giant branch (RGB) of some globular clusters (GC) that appears only when color indices including a near ...ultraviolet band (such as Johnson U or Strömgren u) are considered. This anomalous spread in color indexes such as U − B or cy has been shown to correlate with variations in the abundances of light elements such as C, N, O, Na, etc., which, in turn, are generally believed to be associated with subsequent star formation episodes that occurred in the earliest few 108 yr of the cluster’s life. Here we use publicly available u, g, r Sloan Digital Sky Survey photometry to search for anomalous u − g spreads in the RGBs of nine Galactic GCs. In seven of them (M 2, M 3, M 5, M 13, M 15, M 92 and M 53), we find evidence of a statistically significant spread in the u − g color, not seen in g − r and not accounted for by observational effects. In the case of M 5, we demonstrate that the observed u − g color spread correlates with the observed abundances of Na, the redder stars being richer in Na than the bluer ones. In all the seven clusters displaying a significant u − g color spread, we find that the stars on the red and blue sides of the RGB, in (g, u − g) color magnitude diagrams, have significantly different radial distributions. In particular, the red stars (generally identified with the second generation of cluster stars, in the current scenario) are always more centrally concentrated than blue stars (generally identified with the first generation) over the range sampled by the data (0.5 rh ≲ r ≲ 5 rh), in qualitative agreement with the predictions of some recent models of the formation and chemical evolution of GCs. Our results suggest that the difference in the radial distribution between first and second generation stars may be a general characteristic of GCs.
Abstract
We present the chemical analysis of 49 giant stars of the globular cluster NGC 2419, using medium resolution spectra collected with the multi-object spectrograph DEIMOS@Keck. Previous ...analysis of this cluster revealed a large dispersion in the line strength of the infrared Ca ii triplet, suggesting an intrinsic star-to-star scatter in its Fe or Ca content. From our analysis, we assess that all the investigated stars share the same Fe/H, Ca/Fe and Ti/Fe abundance ratios, while a large spread in Mg and K abundances is detected. The distribution of Mg/Fe is bimodal, with ∼40 per cent of the observed targets having subsolar Mg/Fe, down to Mg/Fe ∼ −1 dex, a level of Mg deficiency never observed before in globular clusters. It is found that the large dispersion in Mg abundances is likely the main origin of the observed dispersion of the Ca ii triplet lines strengths (that can be erroneously interpreted in terms of Fe or Ca abundance scatter) because Mg plays a relevant role in the atmosphere of giant stars as an electron donor. A strong depletion in the Mg abundance leads to an increase of the line strength of the Ca ii triplet, due to the variation in the electronic pressure, at a constant Fe and Ca abundance. Finally, we detect an anti-correlation between Mg and K abundances, not easily explainable within the framework of the current nucleosynthesis models.
We present new determinations of the iron abundance for 220 stars belonging to the stellar system Terzan 5 in the Galactic bulge. The spectra have been acquired with FLAMES at the Very Large ...Telescope of the European Southern Observatory and DEIMOS at the Keck II Telescope. This is by far the largest spectroscopic sample of stars ever observed in this stellar system. From this data set, a subsample of targets with spectra unaffected by TiO bands was extracted and statistically decontaminated from field stars. Once combined with 34 additional stars previously published by our group, a total sample of 135 member stars covering the entire radial extent of the system has been used to determine the metallicity distribution function of Terzan 5. The iron distribution clearly shows three peaks: a super-solar component at Fe/H Asymptotically = to 0.25 dex, accounting for ~29% of the sample, a dominant sub-solar population at Fe/H Asymptotically = to -0.30 dex, corresponding to ~62% of the total, and a minor (6%) metal-poor component at Fe/H Asymptotically = to -0.8 dex. Such a broad, multi-modal metallicity distribution demonstrates that Terzan 5 is not a genuine globular cluster but the remnant of a much more complex stellar system.
In the context of the ESO-VLT Multi-Instrument Kinematic Survey (MIKiS) of Galactic globular clusters (GGCs), we present the line-of-sight rotation curve and velocity dispersion profile of M5 (NGC ...5904), as determined from the radial velocity of more than 800 individual stars observed out to 700″ (∼5 half-mass radii) from the center. We found one of the cleanest and most coherent rotation patterns ever observed for globular clusters, with a very stable rotation axis (having constant position angle of 145° at all surveyed radii) and a well-defined rotation curve. The density distribution turns out to be flattened in the direction perpendicular to the rotation axis, with a maximum ellipticity of ∼0.15. The rotation velocity peak (∼3 km s−1 in projection) is observed at ∼0.6 half-mass radii, and its ratio with respect to the central velocity dispersion (∼0.3–0.4 at 4 projected half-mass radii) indicates that ordered motions play a significant dynamical role. This result strengthens the growing empirical evidence of the kinematic complexity of GGCs and motivates the need of fundamental investigations of the role of angular momentum in collisional stellar dynamics.
PDF
