scholarly journals Is Fornax 4 the nuclear star cluster of the Fornax dwarf spheroidal galaxy?

2020 ◽  
Vol 495 (4) ◽  
pp. 4518-4528
Author(s):  
S Martocchia ◽  
E Dalessandro ◽  
M Salaris ◽  
S Larsen ◽  
M Rejkuba
Keyword(s):  
Stellar Population ◽  
Hubble Space Telescope ◽  
Detailed Comparison ◽  
Observational Evidence ◽  
Star Cluster ◽  
The Other ◽  
Horizontal Branch ◽  
The Galaxy ◽  
Red Giant

ABSTRACT Fornax 4 is the most distinctive globular cluster in the Fornax dwarf spheroidal. Located close to the centre of the galaxy, more metal-rich and potentially younger than its four companions (namely, Fornax clusters number 1, 2, 3, and 5), it has been suggested to have experienced a different formation than the other clusters in the galaxy. Here, we use Hubble Space Telescope/WFC3 photometry to characterize the stellar population content of this system and shed new light on its nature. By means of a detailed comparison of synthetic horizontal branch and red giant branch with the observed colour–magnitude diagrams, we find that this system likely hosts stellar sub-populations characterized by a significant iron spread up to Δ[Fe/H] ∼ 0.4 dex and possibly by also some degree of He abundance variations ΔY ∼ 0.03. We argue that this purely observational evidence, combined with the other peculiarities characterizing this system, supports the possibility that Fornax 4 is the nuclear star cluster of the Fornax dwarf spheroidal galaxy. A spectroscopic follow-up for a large number of resolved member stars is needed to confirm this interesting result and to study in detail the formation and early evolution of this system and more in general the process of galaxy nucleation.

scholarly journals A New Sample of Thick Disk and Halo Stars

1995 ◽  
Vol 164 ◽  
pp. 386-386
Author(s):  
C. Soubiran ◽  
M.N. Perrin ◽  
R. Cayrel ◽  
E. Chereul
Keyword(s):  
Stellar Population ◽  
Thin Disk ◽  
Thick Disk ◽  
The Other ◽  
Chemical Characteristics ◽  
Fundamental Parameters ◽  
Halo Stars ◽  
Synthetic Spectra ◽  
The Galaxy ◽  
Comparison Stars

The aim of our stellar population study is to investigate the kinematical and chemical characteristics of the thin disk, thick disk and halo of the Galaxy. We have selected 51 stars in 2 astrometric and photometric surveys at l = 42°, b = +79° (Soubiran 1992) and l = 167°, b = +47° (Ojha et al. 1994), on the basis of the Reduced Proper Motion Diagram. They were observed with the 193cm telescope at Observatoire de Haute-Provence, with the CARELEC spectrograph (dispersion of 66Å/mm, FWHM of 3.0Å, range λλ4600 – 5500Å), together with 43 comparison stars with known fundamental parameters. The derivation of Teff, logg and [Fe/H] was done differentially using a grid of synthetic spectra and the comparison stars, as described in Cayrel et al. (1991). Twenty of the target stars were found to be more deficient than −0.5. In the (V, [Fe/H]) distribution, the halo stars are clearly separated from the other stars with a mean of (V, [Fe/H]) ≃ (−210km/s, – 1.4dex). Because of the small size of the sample, it was not possible to discriminate the thick disk from the thin disk. We have taken 200 more spectra, and with these new observations, we hope to be able to deconvolve the 3 populations in the (U, V, W, [Fe/H]) space as we did previously with the (U, V) velocity (Soubiran 1993).

scholarly journals The multipopulation phenomenon in Galactic globular clusters: M4 and M22

2009 ◽  
Vol 5 (S266) ◽  
pp. 326-332
Author(s):  
S. Villanova ◽  
G. Piotto ◽  
A. F. Marino ◽  
A. P. Milone ◽  
A. Bellini ◽  
...  
Keyword(s):  
High Resolution ◽  
Spectroscopic Data ◽  
Globular Clusters ◽  
Stellar Population ◽  
The Other ◽  
Wide Field ◽  
Galactic Globular Clusters ◽  
Red Giant ◽  
Process Elements ◽  
Different Characteristics

AbstractWe present an abundance analysis based on high-resolution spectra of red-giant-branch (RGB) stars in the Galactic globular clusters NGC 6121 (M4) and NGC 6656 (M22). Our aim was to study their stellar population in the context of the multipopulation phenomenon recently discovered to affect some globular clusters. Analysis was performed for the following elements: O, Na, Mg, Al, Ca, Fe, Y, and Ba. Spectroscopic data were completed by high-precision wide-field U BV IC ground-based photometry and HST/ACS observations. For M4, we find a well-defined Na–O anticorrelation composed of two distinct groups of stars with significantly different Na and O content. The two groups of Na-rich and Na-poor stars populate two different regions along the RGB. As regards M22, Na and O follow the well-known anticorrelation found in many other GCs. However, at odds with M4, it appears to be continuous without any hint of clumpiness. On the other hand, we identified two clearly separated groups of stars with significantly different abundances of the s-process elements Y, Zr and Ba. The relative numbers of the members of both groups are very similar to the ratio of the stars in the two subgiant branches of M22 recently found by Piotto (2009). The s-element-rich stars are also richer in iron and have higher Ca abundances. This makes M22 the second cluster after ω Centauri where an intrinsic spread in Fe was found. Both spectroscopic and photometric results imply the presence of two stellar populations in M4 and M22, even if both clusters have completely different characteristics.

scholarly journals How Oxygen Affects the CMDs and Predicted Ages of Extreme Population II Stars

2002 ◽  
Vol 12 ◽  
pp. 439-441 ◽  
Author(s):  
Don A. VandenBerg ◽  
R.A. Bell
Keyword(s):  
The Other ◽  
Evolutionary Models ◽  
Horizontal Branch ◽  
Branch Model ◽  
Red Giant

AbstractStellar evolutionary models for [Fe/H] = −2.27 have been constructed to examine how predicted C-M diagrams, age versus turnoff-luminosity relations, the luminosities of the red-giant “bump” and tip, and theTeff/color of a zero-age horizontal branch model of fixed mass are affected by varying the assumed abundance of oxygen (with and without enhancements in the other α-elements).

scholarly journals Identifying Circumgalactic Medium Absorption in QSO Spectra: A Bayesian Approach

2021 ◽  
Vol 923 (1) ◽  
pp. 44
Author(s):  
Jennifer E. Scott ◽  
Emileigh S. Shoemaker ◽  
Colin D. Hamill
Keyword(s):  
Bayesian Methods ◽  
Statistical Approach ◽  
Hubble Space Telescope ◽  
Spectroscopic Studies ◽  
Photometric Data ◽  
Sloan Digital Sky Survey ◽  
Sky Survey ◽  
The Galaxy ◽  
Circumgalactic Medium

Abstract We present a study of candidate galaxy–absorber pairs for 43 low-redshift QSO sightlines (0.06 < z < 0.85) observed with the Hubble Space Telescope/Cosmic Origins Spectrograph that lie within the footprint of the Sloan Digital Sky Survey with a statistical approach to match absorbers with galaxies near the QSO lines of sight using only the SDSS Data Release 12 photometric data for the galaxies, including estimates of their redshifts. Our Bayesian methods combine the SDSS photometric information with measured properties of the circumgalactic medium to find the most probable galaxy match, if any, for each absorber in the line-of-sight QSO spectrum. We find ∼630 candidate galaxy–absorber pairs using two different statistics. The methods are able to reproduce pairs reported in the targeted spectroscopic studies upon which we base the statistics at a rate of 72%. The properties of the galaxies comprising the candidate pairs have median redshift, luminosity, and stellar mass, all estimated from the photometric data, z = 0.13, L = 0.1L *, and log ( M * / M ⊙ ) = 9.7 . The median impact parameter of the candidate pairs is ∼430 kpc, or ∼3.5 times the galaxy virial radius. The results are broadly consistent with the high Lyα covering fraction out to this radius found in previous studies. This method of matching absorbers and galaxies can be used to prioritize targets for spectroscopic studies, and we present specific examples of promising systems for such follow-up.

scholarly journals The Distance and Dynamical History of the Virgo Cluster Ultradiffuse Galaxy VCC 615

2022 ◽  
Vol 924 (2) ◽  
pp. 87
Author(s):  
J. Christopher Mihos ◽  
Patrick R. Durrell ◽  
Elisa Toloba ◽  
Patrick Côté ◽  
Laura Ferrarese ◽  
...  
Keyword(s):  
Dwarf Galaxy ◽  
Hubble Space Telescope ◽  
Virgo Cluster ◽  
Cluster Center ◽  
Main Body ◽  
The Galaxy ◽  
Orbit Modeling ◽  
History Of ◽  
Red Giant ◽  
Distance Estimator

Abstract We use deep Hubble Space Telescope imaging to derive a distance to the Virgo Cluster ultradiffuse galaxy (UDG) VCC 615 using the tip of the red giant branch (TRGB) distance estimator. We detect 5023 stars within the galaxy, down to a 50% completeness limit of F814W ≈ 28.0, using counts in the surrounding field to correct for contamination due to background sources and Virgo intracluster stars. We derive an extinction-corrected F814W tip magnitude of m tip , 0 = 27.19 − 0.05 + 0.07 , yielding a distance of d = 17.7 − 0.4 + 0.6 Mpc. This places VCC 615 on the far side of the Virgo Cluster (d Virgo = 16.5 Mpc), at a Virgocentric distance of 1.3 Mpc and near the virial radius of the main body of Virgo. Coupling this distance with the galaxy’s observed radial velocity, we find that VCC 615 is on an outbound trajectory, having survived a recent passage through the inner parts of the cluster. Indeed, our orbit modeling gives a 50% chance the galaxy passed inside the Virgo core (r < 620 kpc) within the past gigayear, although very close passages directly through the cluster center (r < 200 kpc) are unlikely. Given VCC 615's undisturbed morphology, we argue that the galaxy has experienced no recent and sudden transformation into a UDG due to the cluster potential, but rather is a long-lived UDG whose relatively wide orbit and large dynamical mass protect it from stripping and destruction by the Virgo cluster tides. Finally, we also describe the serendipitous discovery of a nearby Virgo dwarf galaxy projected 90″ (7.2 kpc) away from VCC 615.

scholarly journals Statistical Study of Globules Projected on Stellar Clouds

1958 ◽  
Vol 8 ◽  
pp. 949-950
Author(s):  
D. A. Rojkovsky
Keyword(s):  
Stellar Population ◽  
Milky Way ◽  
Statistical Study ◽  
The Other ◽  
Hot Stars ◽  
Dark Clouds ◽  
Physical Conditions ◽  
Irregular Shapes ◽  
The Galaxy ◽  
Favorable Conditions

The discovery of globules by Bok and Reilly leads to various speculation concerning their cosmogonical meaning as protostellar bodies in our galaxy.It is well known that the most favorable conditions for the discovery and study of globules are reached when they are connected with diffuse galactic nebulae (Dufay). Observations show that in this case globules possess various and generally irregular shapes. It is quite probable that these globules are connected with large dark clouds, genetically linked with bright nebulae. The number of globules in a nebula depends essentially on the peculiarity of its structure. Nevertheless the total area of the sky covered by the nebulae is relatively small and their physical conditions depending on nearby hot stars are peculiar. Consequently it is hardly possible to suppose that the properties of globules present in nebulae are the same as in the other regions of the galaxy. It is important to collect more data concerning the spatial distribution of globules, their density, sizes etc. The stellar clouds of the Milky Way give some possibility for further study in this respect. In the case of a sufficiently dense stellar field the projecting globules can be discovered as some fluctuations in the stellar population as observed on the photograph.

scholarly journals The Stellar Populations of M32: Resolving the nearest elliptical with HST ACS/HRC

2009 ◽  
Vol 5 (S262) ◽  
pp. 135-138 ◽  
Author(s):  
Antonela Monachesi ◽  
S. C. Trager ◽  
Tod R. Lauer ◽  
Wendy Freedman ◽  
Alan Dressler ◽  
...  
Keyword(s):  
Stellar Population ◽  
Asymptotic Giant Branch ◽  
Asymptotic Giant Branch Stars ◽  
Horizontal Branch ◽  
Horizontal Branch Stars ◽  
Magnitude Diagram ◽  
Colour Distribution ◽  
Red Clump ◽  
Red Giant ◽  
Giant Branch Stars

AbstractWe present the deepest colour-magnitude diagram (CMD) of M32 to date, obtained from deep (F435W, F555W) photometry of HST ACS/HRC images. Due to the high resolution of our images, the small photometric errors, and the completeness level of our data we obtain the most detailed resolved photometric study of M32 to date. The CMD of M32 displays a wide colour distribution of red giant branch stars, mainly due to a metallicity spread, a strong red clump and bright asymptotic giant branch stars. The detection of a “blue plume” in M32 indicates the presence of a very young stellar population. There is not a noticeable presence of blue horizontal branch stars, suggesting that an old population with [Fe/H] < −1.5 does not significantly contribute to the light or mass of M32 in our observed fields.

scholarly journals An overall picture of EMP stars using the stellar abundances for galactic archaeology (SAGA) database

2009 ◽  
Vol 5 (S265) ◽  
pp. 90-93
Author(s):  
Takuma Suda ◽  
Shimako Yamada ◽  
Yutaka Katsuta ◽  
Chikako Ishizuka ◽  
Yutaka Komiya ◽  
...  
Keyword(s):  
Early Phase ◽  
Globular Clusters ◽  
The Other ◽  
Stellar Abundances ◽  
Mixing Processes ◽  
Lithium Abundance ◽  
Other Hand ◽  
The Galaxy ◽  
Order Of Magnitude ◽  
Red Giant

AbstractWe explore the general characteristics of extremely metal-poor (EMP) stars in the Galaxy using the Stellar Abundances for Galactic Archaeology (SAGA) database (Suda et al. 2008, PASJ, 60, 1159). The overall trend of EMP stars suggests that there are at least two types of extra mixing to change the surface abundances of EMP stars. One is to deplete lithium abundance during the early phase of giant branch and another is to decrease C/N ratio by one order of magnitude during the red giant branch or AGB phase. On the other hand, these mixing processes are different from those suggested in the Galactic globular clusters because of the different relations between O, Na, Mg, and Al abundances.

scholarly journals Planets, evolved stars, and how they might influence each other.

2011 ◽  
Vol 7 (S283) ◽  
pp. 219-226 ◽  
Author(s):  
Eva Villaver
Keyword(s):  
White Dwarfs ◽  
Main Sequence ◽  
Planetary Nebulae ◽  
The Other ◽  
Horizontal Branch ◽  
Low Mass Stars ◽  
Evolved Stars ◽  
Low Mass ◽  
Red Giant

AbstractOver the last 20 years planetary searches have revealed a wealth of systems orbiting stars on the main sequence. Most of these low-mass stars eventually will evolve into the Giant phases before entering the planetary nebulae (PNe) stage. In the last years, the presence of planets has also been discovered around more massive evolved stars, mostly, along the Red Giant but also along the Horizontal Branch. Moreover, disks have been found around White Dwarfs presumably formed by tidally disrupted asteroids. In all, there is evidence that an evolved (ing) star might influence the survival of planets. In this review I will try to summarize such evidence but furthermore I will present the other side of the story, that is, how the presence of a planet might alter the evolution of stars and with that the PN formation.

scholarly journals Influence of Planets on Parent Stars: Angular Momentum

2004 ◽  
Vol 219 ◽  
pp. 323-332
Author(s):  
Noam Soker
Keyword(s):  
Angular Momentum ◽  
Globular Clusters ◽  
Hubble Space Telescope ◽  
Mass Loss Rate ◽  
Planetary Nebulae ◽  
Asymptotic Giant Branch ◽  
Tidal Interaction ◽  
Evolved Stars ◽  
The Galaxy ◽  
Red Giant

I review some possible processes by which planets and brown dwarfs can influence the evolution of their parent evolved stars. As sunlike stars evolve on the red giant branch (RGB) and then on the asymptotic giant branch (AGB), they will interact with their close planets (if exist). The interaction starts with tidal interaction: this will lead the planets to deposit most of their angular momentum to the envelope of the giant, and then spiral-in to the envelope. (Too many papers dealing with close planets [less than about 3-6 AU] around evolved stars neglect tidal interaction, hence their results are questionable.) They may spin-up their parent stars by up to several orders of magnitude. The interaction of substellar objects with evolved star may enhance the mass loss rate, mainly in the equatorial plane. Possible outcomes are: (i) Planetary systems interacting with their parent AGB star may lead to the formation of moderate elliptical planetary nebulae. (ii) RGB stars which lose more mass turn to bluer horizontal branch (HB) stars. Therefore, planets may explain the formation of blue HB stars. This may explain the presence of many blue HB stars in many globular clusters (the planets be the second parameter), and some hot HB stars in the galaxy (sdB stars). (The 8.3 days use of the Hubble Space Telescope in search of planets in a globular clusters with no blue HB stars was a wrong move.) (iii) Most known stars with planets will not form planetary nebulae, because they will lose most of their envelope already on the RGB.

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