scholarly journals Stellar Populations in the Pegasus Dwarf Galaxy

1995 ◽  
Vol 164 ◽  
pp. 413-413
Author(s):  
Myung Gyoon Lee
Keyword(s):  
Dwarf Galaxy ◽  
Stellar Populations ◽  
Young Stars ◽  
Asymptotic Giant Branch ◽  
Distance Estimate ◽  
Irregular Galaxy ◽  
Ccd Photometry ◽  
Red Supergiants ◽  
The Mean ◽  
Red Giant

The Pegasus dwarf galaxy (DDO 216) is a resolved irregular galaxy. We present a study of stars in this galaxy based on BV RI CCD photometry obtained using the Palomar 1.5m telescope. The color-magnitude diagrams show (a) a dominant red giant branch (RGB) population, (b) a small number of asymptotic giant branch (AGB) population above the tip of the RGB (TRGB), and (c) a sparse popultion of massive young stars including the brightest red supergiants. The mean metallicity of the RGB has been estimated from the color of the RGB at MI = −3.5 mag: [Fe/H] = −1.5 ± 0.2 dex. The distance to this galaxy has been measured using the I-magnitude of the TRGB: (m – M)0 = 25.13 ± 0.11 mag (d = 1060 ± 50 kpc) (see Lee et al. 1993). This value is significantly smaller than the Cepheid distance estimate by Hoessel et al. (1990), (m – M)0 = 26.22±0.20 (d = 1750±160 kpc).

scholarly journals Stellar Populations and Local Group Membership of the Dwarf Galaxy DDO 210

1999 ◽  
Vol 192 ◽  
pp. 268-271
Author(s):  
Myung Gyoon Lee
Keyword(s):  
Stellar Population ◽  
Local Group ◽  
Group Membership ◽  
Dwarf Galaxy ◽  
Stellar Populations ◽  
Young Stars ◽  
Ccd Photometry ◽  
A Value ◽  
Red Giant

Deep BVI CCD photometry of dwarf galaxy DD0 210 obtained in this study shows that the resolved stellar population in this galaxy consists of a dominant old red giant population and some young stars. We have estimated the distance to this galaxy using the I-band magnitude of the tip of the red giant branch, obtaining a value of 1030±50 kpc. This result combined with the velocity of DDO 210 shows that DDO 210 is a member of the Local Group.

scholarly journals Recovering the Star Formation History of IC1613 Dwarf Galaxy Using Evolved Stars

2018 ◽  
Vol 14 (S344) ◽  
pp. 77-80
Author(s):  
Seyed Azim Hashemi ◽  
Atefeh Javadi ◽  
Jacco Th. van Loon
Keyword(s):  
Star Formation ◽  
Dwarf Galaxy ◽  
Stellar Populations ◽  
Asymptotic Giant Branch ◽  
Star Formation History ◽  
Evolved Stars ◽  
Formation History ◽  
The Galaxy ◽  
Red Supergiants ◽  
Period Variable

AbstractDetermining the star formation history (SFH) is key to understand the formation and evolution of dwarf galaxies. Recovering the SFH in resolved galaxies is mostly based on deep colour–magnitude diagrams (CMDs), which trace the signatures of multiple evolutionary stages of their stellar populations. In distant and unresolved galaxies, the integrated light of the galaxy can be decomposed, albeit made difficult by an age–metallicity degeneracy. Another solution to determine the SFH of resolved galaxies is based on evolved stars; these luminous stars are the most accessible tracers of the underlying stellar populations and can trace the entire SFH. Here we present a novel method based on long period variable (LPV) evolved asymptotic giant branch (AGB) stars and red supergiants (RSGs). We applied this method to reconstruct the SFH for IC1613, an irregular dwarf galaxy at a distance of 750 kpc. Our results provide an independent confirmation that no major episode of star formation occurred in IC1613 over the past 5 Gyr.

AGB and RGB stars in the dwarf irregular galaxy Leo A

2021 ◽  
Vol 647 ◽  
pp. A170
Author(s):  
Alina Leščinskaitė ◽  
Rima Stonkutė ◽  
Vladas Vansevičius
Keyword(s):  
Star Formation ◽  
Galaxy Evolution ◽  
Near Infrared ◽  
Dwarf Galaxy ◽  
Asymptotic Giant Branch ◽  
Star Formation History ◽  
Photometric Method ◽  
Agb Stars ◽  
Irregular Galaxy ◽  
Red Giant

Context. Leo A is a gas-rich dwarf irregular galaxy of low stellar mass located in the outskirts of the Local Group. It has an extended star formation history with stellar populations spanning a wide age range (∼0.01−10 Gyr). As Leo A is a well-isolated dwarf galaxy, it is a perfect target to study a galactic structure formed entirely by processes of self-induced star formation. Aims. Our aim is to study populations of the brightest asymptotic giant branch (AGB) stars and red giant branch (RGB) stars over the entire extent of the Leo A galaxy. Methods. We analysed populations of AGB and RGB stars in the Leo A galaxy using multicolour photometry data obtained with the Subaru Suprime-Cam (B, V, R, I, Hα) and HST ACS (F475W, F814W) cameras. In order to separate the Milky Way and Leo A populations of red stars, we developed a photometric method that enabled us to study the spatial distribution of AGB and RGB stars within the Leo A galaxy. Results. We found a previously unknown sequence of 26 peculiar RGB stars which probably have a strong CN band in their spectra (∼380−390 nm). This conclusion is supported by the infrared CN spectral features observed in four of these stars with available spectra from the literature. Additionally, we present a catalogue of 32 luminous AGB stars and 3 candidate AGB stars. Twelve AGB stars (three of them might have dusty envelopes) from this sample are newly identified; the remaining 20 AGB stars were already presented in the literature based on near-infrared observations. By splitting the RGB sequence into blue and red parts, we revealed different spatial distributions of the two subsets, with the former being more centrally concentrated than the latter. Cross-identification with spectroscopic data available in the literature suggests that the bulk of blue and red RGB stars are, on average, similar in metallicity; however, the red RGB stars might have an excess of metal-deficient stars of [Fe/H] < −1.8. We also found that the distributions of luminous AGB and blue RGB stars have nearly equal scale lengths (0.′87 ± 0.′06 and 0.′89 ± 0.′09, respectively), indicating that they could belong to the same generation. This conclusion is strengthened by the similarities of the cumulative distributions of AGB and blue RGB stars, both showing more centrally concentrated populations compared to red RGB stars. There is also a prominent decline in the ratio of AGB to RGB stars with an increasing radius. These results suggest that the star-forming disk of Leo A is shrinking, which is in agreement with the outside-in star formation scenario of dwarf galaxy evolution.

scholarly journals On the precision of full-spectrum fitting of simple stellar populations – I. Well-sampled populations

2020 ◽  
Vol 498 (2) ◽  
pp. 2814-2832
Author(s):  
Randa Asa’d ◽  
Paul Goudfrooij
Keyword(s):  
Random Noise ◽  
Star Clusters ◽  
Stellar Populations ◽  
Asymptotic Giant Branch ◽  
Full Spectrum ◽  
Red Giant ◽  
Set Up ◽  
Age Range ◽  
Spectrum Fitting ◽  
Giant Branch Stars

ABSTRACT We investigate the precision of the ages and metallicities of 21 000 mock simple stellar populations (SSPs) determined through full-spectrum fitting. The mock SSPs cover an age range of 6.8 &lt; log (age/yr) &lt; 10.2, for three wavelength ranges in the optical regime, using both Padova and MIST isochrone models. Random noise is added to the model spectra to achieve S/N ratios between 10 and 100 per wavelength pixel. We find that for S/N ≥ 50, this technique can yield ages of SSPs to an overall precision of ∆log (age/yr)∼01 for ages in the ranges 7.0 ≤ log (age/yr) ≤ 8.3 and 8.9 ≤ log (age/yr) ≤ 9.4. For the age ranges of 8.3 ≤ log (age/yr) ≤ 8.9 and log (age/yr) ≥ 9.5, which have significant flux contributions from asymptotic giant branch and red giant branch stars, respectively, the age uncertainty rises to about ±0.3 dex. The precision of age and metallicity estimation using this method depends significantly on the S/N and the wavelength range used in the fitting. We quantify the systematic differences in age predicted by the MIST and Padova isochrone models, due to their different assumptions about stellar physics in various important (i.e. luminous) phases of stellar evolution, which needs to be taken in consideration when comparing ages of star clusters obtained using these popular models. Knowing the strengths and limitations of this technique is crucial in interpreting the results obtained for real star clusters and for deciding the optimal instrument set-up before performing the observations.

scholarly journals The dwarf galaxy satellite system of Centaurus A

2019 ◽  
Vol 629 ◽  
pp. A18 ◽  
Author(s):  
Oliver Müller ◽  
Marina Rejkuba ◽  
Marcel S. Pawlowski ◽  
Rodrigo Ibata ◽  
Federico Lelli ◽  
...  
Keyword(s):  
Luminosity Function ◽  
Local Group ◽  
Dwarf Galaxies ◽  
Dwarf Galaxy ◽  
3D Structure ◽  
Major Axis ◽  
Asymptotic Giant Branch ◽  
Semi Major Axis ◽  
Distance Measurements ◽  
Red Giant

Dwarf galaxy satellite systems are essential probes to test models of structure formation, making it necessary to establish a census of dwarf galaxies outside of our own Local Group. We present deep FORS2 VI band images from the ESO Very Large Telescope (VLT) for 15 dwarf galaxy candidates in the Centaurus group of galaxies. We confirm nine dwarfs to be members of Cen A by measuring their distances using a Bayesian approach to determine the tip of the red giant branch luminosity. We have also fit theoretical isochrones to measure their mean metallicities. The properties of the new dwarfs are similar to those in the Local Group in terms of their sizes, luminosities, and mean metallicities. Within our photometric precision, there is no evidence of a metallicity spread, but we do observe possible extended star formation in several galaxies, as evidenced by a population of asymptotic giant branch stars brighter than the red giant branch tip. The new dwarfs do not show any signs of tidal disruption. Together with the recently reported dwarf galaxies by the complementary PISCeS survey, we study the luminosity function and 3D structure of the group. By comparing the observed luminosity function to the high-resolution cosmological simulation IllustrisTNG, we find agreement within a 90% confidence interval. However, Cen A seems to be missing its brightest satellites and has an overabundance of the faintest dwarfs in comparison to its simulated analogs. In terms of the overall 3D distribution of the observed satellites, we find that the whole structure is flattened along the line-of-sight, with a root-mean-square (rms) height of 130 kpc and an rms semi-major axis length of 330 kpc. Future distance measurements of the remaining dwarf galaxy candidates are needed to complete the census of dwarf galaxies in the Centaurus group.

scholarly journals Near-Infrared Stellar Populations in the metal-poor, Dwarf irregular Galaxies Sextans A and Leo A

2018 ◽  
Vol 14 (S343) ◽  
pp. 429-430
Author(s):  
Olivia C. Jones ◽  
Matthew T. Maclay ◽  
Martha L. Boyer ◽  
Margaret Meixner ◽  
Iain McDonald
Keyword(s):  
Near Infrared ◽  
Infrared Camera ◽  
Stellar Populations ◽  
Asymptotic Giant Branch ◽  
Evolved Stars ◽  
Irregular Galaxies ◽  
Tentative Evidence ◽  
Period Variable ◽  
Red Giant ◽  
Dwarf Irregular Galaxies

AbstractWe present JHK observations of the metal-poor $$(\left[ {{\rm{Fe}}/{\rm{H}}} \right] < - 1.40)$$ dwarf-irregular galaxies, Leo A and Sextans A, obtained with the WIYN High-resolution Infrared Camera. Their near-IR stellar populations are characterized by using a combination of color-magnitude diagrams and by identifying long-period variable (LPV) stars. We detected red giant and asymptotic giant branch (AGB) stars, consistent with membership of the galaxy’s intermediate-age populations (2-8 Gyr old). We identify 32 dusty evolved stars in Leo A and 101 dusty stars in Sextans A, confirming that metal-poor stars can form substantial amounts of dust. We also find tentative evidence for oxygen-rich dust formation at low metallicity, contradicting previous models that suggest oxygen-rich dust production is inhibited in metal-poor environments. The majority of this dust is produced by a few very dusty evolved stars.

scholarly journals Nearby Blue Compact Dwarf Galaxy NGC 6789

1999 ◽  
Vol 192 ◽  
pp. 253-258
Author(s):  
I. Drozdovsky ◽  
N. Tikhonov
Keyword(s):  
Surface Brightness ◽  
Dwarf Galaxy ◽  
High Surface ◽  
Low Surface Brightness ◽  
The Galaxy ◽  
Metal Abundance ◽  
The Mean ◽  
Red Giant ◽  
Halo Population ◽  
Blue Compact Dwarf Galaxy

We present the results of a detailed BVRI and Hα study of the isolated nearby blue compact dwarf (BCD) galaxy NGC 6789. Judging from the literature the observed galaxy has not yet been resolved into stars up to now. On CCD frames obtained with 6m BTA telescope and 2.5m Nordic telescope the galaxy is well resolved. Its colour-magnitude diagram confirms the two component (core-halo) galaxy morphology, which consists of two stellar populations distinct in structure and colour: an inner high surface-brightness young population within 150 pc from the center of the galaxy, and a relatively low surface-brightness intermediate-age population extending out to at least 600 pc. The distance to the galaxy, estimated from the tip of the red giant branch (TRGB) is 2.1 Mpc which places NGC 6789 close to the Local Group. From the mean colour of the RGB, the mean metal abundance of the halo population is estimated as [Fe/H] ≃ −1 dex.

scholarly journals The chemical evolution of the dwarf spheroidal galaxy Sextans

2020 ◽  
Vol 642 ◽  
pp. A176 ◽  
Author(s):  
R. Theler ◽  
P. Jablonka ◽  
R. Lucchesi ◽  
C. Lardo ◽  
P. North ◽  
...  
Keyword(s):  
Star Formation ◽  
Galaxy Evolution ◽  
Dwarf Galaxy ◽  
Small Mass ◽  
Asymptotic Giant Branch ◽  
Asymptotic Giant Branch Stars ◽  
Chemical Abundances ◽  
Low Metallicity ◽  
Red Giant ◽  
Giant Branch Stars

We present our analysis of the FLAMES dataset targeting the central 25′ region of the Sextans dwarf spheroidal galaxy (dSph). This dataset is the third major part of the high-resolution spectroscopic section of the ESO large program 171.B-0588(A) obtained by the Dwarf galaxy Abundances and Radial-velocities Team. Our sample is composed of red giant branch stars down to V ∼ 20.5 mag, the level of the horizontal branch in Sextans, and allows users to address questions related to both stellar nucleosynthesis and galaxy evolution. We provide metallicities for 81 stars, which cover the wide [Fe/H] = −3.2 to −1.5 dex range. The abundances of ten other elements are derived: Mg, Ca, Ti, Sc, Cr, Mn, Co, Ni, Ba, and Eu. Despite its small mass, Sextans is a chemically evolved system, showing evidence of a contribution from core-collapse and Type Ia supernovae as well as low-metallicity asymptotic giant branch stars (AGBs). This new FLAMES sample offers a sufficiently large number of stars with chemical abundances derived with high accuracy to firmly establish the existence of a plateau in [α/Fe] at ∼0.4 dex followed by a decrease above [Fe/H] ∼ −2 dex. These features reveal a close similarity with the Fornax and Sculptor dSphs despite their very different masses and star formation histories, suggesting that these three galaxies had very similar star formation efficiencies in their early formation phases, probably driven by the early accretion of smaller galactic fragments, until the UV-background heating impacted them in different ways. The parallel between the Sculptor and Sextans dSph is also striking when considering Ba and Eu. The same chemical trends can be seen in the metallicity region common to both galaxies, implying similar fractions of SNeIa and low-metallicity AGBs. Finally, as to the iron-peak elements, the decline of [Co/Fe] and [Ni/Fe] above [Fe/H] ∼ −2 implies that the production yields of Ni and Co in SNeIa are lower than that of Fe. The decrease in [Ni/Fe] favours models of SNeIa based on the explosion of double-degenerate sub-Chandrasekhar mass white dwarfs.

scholarly journals Surveys for Field Carbon Stars in the Magellanic Clouds

1994 ◽  
Vol 161 ◽  
pp. 509-512 ◽  
Author(s):  
M. Azzopardi ◽  
E. Rebeirot ◽  
B.E. Westerlund
Keyword(s):  
Stellar Population ◽  
Magellanic Clouds ◽  
Asymptotic Giant Branch ◽  
Carbon Stars ◽  
Dwarf Spheroidal Galaxies ◽  
Giant Stars ◽  
Intermediate Mass Stars ◽  
Nearest Neighbours ◽  
The Mean ◽  
Red Giant

The Asymptotic Giant Branch (AGB) stage is the normal luminous phase of evolution of intermediate-mass stars (slightly less than 1 M ⊙ up to very roughly 3 M ⊙) and therefore the AGB stars play a noteworthy role in our understanding of the chemical evolution of galactic systems. Furthermore it is now generally accepted that the ratio of carbon (C) stars to late-type M giant stars can be used to estimate the mean metallicity of the stellar population of a system, or the change in metallicity from the inner to the outer parts of a galaxy. It is for these reasons among others that red giant stars have been searched for in nearby local group galaxies, principally in our nearest neighbours, the Magellanic Clouds and the dwarf spheroidal galaxies. This paper will be particularly devoted to the slitless spectroscopy surveys for carbon stars in the Magellanic Clouds.

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