81 research outputs found
Its moderately extended low-density halo and its accretion history
We present results based on Dark Energy Camera Legacy Survey (DECaLS) DR8 astrometric and photometric data sets of the Milky Way globular cluster Pal 13. Because of its relatively small size and mass, there is not yet a general consensus on the existence of extra-tidal structures surrounding it. While some previous results suggest the absence of such features, others show that the cluster is under the effects of tidal stripping. We have built a cluster stellar density map from DECaLS g, r magnitudes-previously corrected for interstellar reddening-of stars placed along the cluster main sequence in the color-magnitude diagram. The resulting density map shows nearly smooth contours around Pal 13 out to approximately 1.6 t the most recent estimate of its Jacobi radius, which was derived whilst taking into account the variation along its orbital motion. This outcome favors the presence of stars escaping the cluster, a phenomenon frequently seen in globular clusters that have crossed the Milky Way disk a comparably large number of times. Particularly, the orbital high eccentricity and large inclination angle of this accreted globular cluster could have been responsible for the relatively large amount of lost cluster mass.Fil: Piatti, Andres Eduardo. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Conicet - Córdoba. Instituto de AstronomÃa Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de AstronomÃa Teórica y Experimental; ArgentinaFil: Fernández Trincado, José G.. Universidad de Atacama; Chil
Near-infrared chemical abundances of stars in the Sculptor dwarf galaxy
Owing to the recent identification of major substructures in our Milky Way
(MW), the astronomical community has started to reevaluate the importance of
dissolved and existing dwarf galaxies. In this work, we investigate up to 13
elements in 43 giant stars of the Sculptor dwarf galaxy (Scl) using
high-signal-to-noise-ratio near-infrared (NIR) APOGEE spectra. Thanks to the
strong feature lines in the NIR, we were able to determine high-resolution O,
Si, and Al abundances for a large group of sample stars for the first time in
Scl. By comparing the [/Fe] (i.e., O, Mg, Si, Ca, and Ti) of the stars
in Scl, Sagittarius, and the MW, we confirm the general trend that less massive
galaxies tend to show lower [/Fe]. The low [Al/Fe] () in Scl
demonstrates the value of this ratio as a discriminator with which to identify
stars born in dwarf galaxies (from MW field stars). A chemical-evolution model
suggests that Scl has a top-light initial mass function (IMF), with a high-mass
IMF power index of , and a minimum Type Ia supernovae delay time of
Myr. Furthermore, a linear regression analysis indicates a negative
radial metallicity gradient and positive radial gradients for [Mg/Fe] and
[Ca/Fe], in qualitative agreement with the outside-in formation scenario.Comment: A&A accepte
Exploring the short-term variability of H and H emissions in a sample of M dwarfs
The time scales of variability in active M dwarfs can be related to their
various physical parameters. Thus, it is important to understand such
variability to decipher the physics of these objects. In this study, we have
performed the low resolution (5.7\AA) spectroscopic monitoring of 83 M
dwarfs (M0-M6.5) to study the variability of H / H emissions;
over the time scales from 0.7 to 2.3 hours with a cadence of 3-10
minutes. Data of a sample of another 43 late-type M dwarfs (M3.5-M8.5) from the
literature are also included to explore the entire spectral sequence. 53 of the
objects in our sample (64\%) show statistically significant short-term
variability in H. We show that this variability in 38 of them are most
likely to be related to the flaring events. We find that the early M dwarfs are
less variable despite showing higher activity strengths
(L/L \& L/L), which saturates around
10 for M0-M4 types. Using archival photometric light curves from
TESS and Kepler/K2 missions, the derived chromospheric emission (\ha and \hb
emission) variability is then explored for any plausible systematics with
respect to their rotation phase. The variability indicators clearly show higher
variability in late-type M dwarfs (M5-M8.5) with shorter rotation periods (2
days). For 44 sources, their age has been estimated using StarHorse project and
possible correlations with variability have been explored. The possible causes
and implications for these behaviors are discussed.Comment: There are 35 pages including 18 pages of supplementary material. The
manuscript is accepted for publication in MNRA
On the identification of N-rich metal-poor field stars with future China space station telescope
During the long term evolution of globular clusters (GCs), a part of member
stars are lost to the field. The recently found nitrogen-rich (N-rich)
metal-poor field stars are promising candidates of these GC escapees, since N
enhancement is the fingerprint of chemically enhanced populations in GCs. In
this work, we discuss the possibility of identifying N-rich metal-poor field
stars with the upcoming China space station telescope (CSST). We focus on the
main survey camera with NUV, u, g, r, i, z, y filters and slitless spectrograph
with a resolution about 200. The combination of UV sensitive equipment and
prominent N-related molecular lines in the UV band bodes well for the
identification: the color-color diagram of (u-g) versus (g-r) is capable of
separating N-rich field stars and normal halo stars, if metallicity can be
estimated without using the information of u-band photometry. Besides, the
synthetic spectra show that a signal-to-noise ratio of 10 is sufficient to
identify N-rich field stars. In the near future, a large sample of N-rich field
stars found by CSST, combined with state-of-the-art N-body simulations will be
crucial to decipher the GC-Galaxy co-evolution.Comment: 13+2 pages, 11+2 figures, 4 tables, accepted by RA
A peculiar interacting Be star binary in the Small Magellanic Cloud
We find that the emission-line object OGLEJ005039.05-725751.4, a member of the cluster OGLE-CL SMC 64, exhibits a peculiar light curve pattern repeating with a recurrence time of 141.45 days. The light curve resembles periodic outbursts with a duty cycle of 20%. A second long cycle of 2500 days is also detected in the photometric data set. Two X-SHOOTER spectra obtained at minimum and maximum reveal a Be star dominating at minimum light resembling the Classical Be star 48 Lib. The larger Hα emission, the stronger Na D absorption and the appearance of emission in the infrared Ca II triplet at maximum, might indicate periodic mass transfer in a complex binary system.Facultad de Ciencias Astronómicas y GeofÃsicasInstituto de AstrofÃsica de La Plat
Age-chemical abundance structure of the Galaxy I:evidence for a late accretion event in the outer disc at z ~ 0.6
Galactic ArchaeoLogIcaL ExcavatiOns (GALILEO) II. t-SNE Portrait of Local Fossil Relics and Structures
Based on high-quality APOGEE DR17 and Gaia DR3 data for 1,742 red giants
stars within 5 kpc of the Sun and not rotating with the Galactic disc ( 100 km s), we use the nonlinear technique of unsupervised analysis
t-SNE to detect coherent structures in the space of ten chemical-abundance
ratios: [Fe/H], [O/Fe], [Mg/Fe], [Si/Fe], [Ca/Fe], [C/Fe], [N/Fe], [Al/Fe],
[Mn/Fe], and [Ni/Fe]. Additionally, we obtain orbital parameters for each star
using the non-axisymmetric gravitational potential {\tt GravPot16}. Seven
structures are detected, including the Splash, Gaia-Sausage-Enceladus (GSE),
the high- heated-disc population, N-C-O peculiar stars, and inner
disk-like stars, plus two other groups that did not match anything previously
reported in the literature, here named Galileo 5 and Galileo 6 (G5 and G6).
These two groups overlap with Splash in [Fe/H], G5 being lower metallicity than
G6, both between GSE and Splash in the [Mg/Mn] versus [Al/Fe] plane, G5 in the
-rich in-situ locus, and G6 on the border of the -poor in-situ
one; nonetheless their low [Ni/Fe] hints to a possible ex-situ origin. Their
orbital energy distributions are between the Splash and GSE, with G5 being
slightly more energetic than G6. We verified the robustness of all the obtained
groups by exploring a large range of t-SNE parameters, applying it to various
subsets of data, and also measuring the effect of abundance errors through
Monte Carlo tests.Comment: Accepted by A&A. 19 pages, 15 figures, and 3 table
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