Stars In Other Galaxies Research Articles

Infrared photometric study of symbiotic stars

We have searched and collected almost all symbiotic stars up to date from the literature to study their infrared properties mainly including possible infrared excesses and radiation mechanisms. 332 symbiotic stars in total are found including 263 ones in our Galaxy and 69 ones in other galaxies. The observational data from The Two Micron All Sky Survey (2MASS), The Wide-field Infrared Survey Explorer (WISE) and the Infrared Astronomical Satellite (IRAS) are employed to the analysis. It is found that in the near infrared region the radiation of S-type and S+IR-type symbiotic stars is mainly due to the thermal emission from dust/stellar photosphere while the radiation of D-type and D’-type symbiotic stars is mainly due to the free-free/bound-free emission from the stellar wind. However, in the W1W2W3 region the infrared radiation of S-type, S+IR-type and D’-type stars is mainly due to the free-free/bound-free emission from the stellar wind while the infrared radiation of D-type stars is due to the thermal emission from the silicate dust. In the W2W3W4 region the radiation of almost all stars is from the free-free/bound-free emissions from the stellar wind, but in the IRAS region the radiation of almost all stars is from dust thermal emissions at the far distance. In addition, the infrared mechanism and emission status of symbiotic stars in other galaxies are also presented and the comparison with that for symbiotic stars in our Galaxy is made.

Sulphur in the Sculptor dwarf spheroidal galaxy

In Galactic halo stars, sulphur has been shown to behave like other $\alpha$-elements, but until now, no comprehensive studies have been done on this element in stars of other galaxies. Here, we use high-resolution ESO VLT/FLAMES/GIRAFFE spectra to determine sulphur abundances for 85 stars in the Sculptor dwarf spheroidal galaxy, covering the metallicity range $-2.5\leq \text{[Fe/H]} \leq-0.8$. The abundances are derived from the S~I triplet at 9213, 9228, and 9238~\AA. These lines have been shown to be sensitive to departure from local thermodynamic equilibrium, i.e. NLTE effects. Therefore, we present new NLTE corrections for a grid of stellar parameters covering those of the target stars. The NLTE-corrected sulphur abundances in Sculptor show the same behaviour as other $\alpha$-elements in that galaxy (such as Mg, Si, and Ca). At lower metallicities ($\text{[Fe/H]}\lesssim-2$) the abundances are consistent with a plateau at $\text{[S/Fe]}\approx+0.16$, similar to what is observed in the Galactic halo, $\text{[S/Fe]}\approx+0.2$. With increasing [Fe/H], the [S/Fe] ratio declines, reaching negative values at $\text{[Fe/H]}\gtrsim-1.5$. The sample also shows an increase in [S/Mg] with [Fe/H], most probably because of enrichment from Type Ia supernovae.

The Wolf-Rayet stars in M 31

Context: Comprehensive studies of Wolf-Rayet stars were performed in the past for the Galactic and the LMC population. The results revealed significant differences, but also unexpected similarities between the WR populations of these different galaxies. Analyzing the WR stars in M31 will extend our understanding of these objects in different galactic environments. Aims: The present study aims at the late-type WN stars in M31. The stellar and wind parameters will tell about the formation of WR stars in other galaxies with different metallicity and star formation histories. The obtained parameters will provide constraints to the evolution of massive stars in the environment of M31. Methods: We used the latest version of the Potsdam Wolf-Rayet model atmosphere code to analyze the stars via fitting optical spectra and photometric data. To account for the relatively low temperatures of the late WN10 and WN11 subtypes, our WN models have been extended into this temperature regime. Results: Stellar and atmospheric parameters are derived for all known late-type WN stars in M31 with available spectra. All of these stars still have hydrogen in their outer envelopes, some of them up to 50% by mass. The stars are located on the cool side of the zero age main sequence in the Hertzsprung-Russell diagram, while their luminosities range from $10^5$ to $10^6$ Lsun. It is remarkable that no star exceeds $10^6$ Lsun. Conclusions: If formed via single-star evolution, the late-type WN stars in M31 stem from an initial mass range between 20 and 60 Msun. From the very late-type WN9-11 stars, only one star is located in the S Doradus instability strip. We do not find any late-type WN stars with the high luminosities known in the Milky Way.

The young stellar population of IC 1613

<i>Context. <i/>Determining the parameters of massive stars is crucial to understand many processes in galaxies and the Universe, since these objects are important sources of ionization, chemical enrichment and momentum. 10m class telescopes enable us to perform detailed quantitative spectroscopic analyses of massive stars in other galaxies, sampling areas of different metallicity. Relating the stars to their environment is crucial to understand the physical processes ruling their formation and evolution. <i>Aims. <i/>In preparation for the new instrumentation planned for the <i>Gran Telescopio CANARIAS<i/> (GTC), our goal is to build a list of massive star candidates in the metal-poor irregular galaxy IC 1613. The catalogue must have very high astrometric accuracy, suitable for the current generation of multi-object spectrographs. A census of OB associations in this galaxy is also needed, to provide important additional information about the age and environment of the candidate OB stars. <i>Methods. <i/>From observations taken with the Wide Field Camera (WFC) at the Isaac Newton Telescope (INT), we have built an astrometric and photometric catalogue of stars in IC 1613. Candidate blue massive stars are preselected by their colors. A friends-of-friends algorithm is developed to find their clustering in the galaxy. While a common physical origin for all the members of the associations cannot be ensured, this is a necessary first step to place candidate OB stars in a population context. <i>Results. <i/>We have produced a deep catalogue of targets in IC 1613 that covers a large field of view. To achieve high astrometric accuracy, a new astrometric procedure was developed for the INT-WFC data. We also built a catalogue of OB associations in IC 1613 and found that they concentrate in the central regions, especially in the H ii bubbles. The study of extinction confirms that it is patchy, with local values of color-excess above the foreground value.

AGB stars in the Magellanic Clouds and in other members of the Local Group

AbstractResults obtained in the Magellanic Clouds using the latest near-IR DENIS survey are briefly reviewed. This sets the stage for a similar study of AGB stars in other galaxies in the Local Group and, in particular, in NGC 6822.

The 5200-A flux depression of chemically peculiar stars -- I. Synthetic a photometry: the normality line

The Δa photometric system provides an efficient observational method to identify and distinguish magnetic and several other types of chemically peculiar (CP) stars of spectral types B to F from other classes of stars in the same range of effective temperatures. We have developed a synthetic photometric system that can be used to explore the capability of model atmospheres with individual element abundances to predict photometric Δa magnitudes, which measure the extent of the flux depression around 5200 A found in different types of CP stars. In this first paper, we confirm the observed dependency of the a index as a function of various colour indices sensitive to the effective temperature of stars as well as its average scatter expected from surface gravity variations within the main-sequence band. The behaviour of the so-called 'normality line' of Δa systems used in photometric observations of CP stars is well reproduced. The metallicity dependence of the normality line of the Δa system was computed for several grids of model atmospheres where the abundances of elements heavier than He had been scaled ′0.5 dex with respect to the solar value. We estimate a lowering of Δa magnitudes for CP stars within the Magellanic Clouds by ∼-3 mmag relative to those in the solar neighbourhood assuming an average metallicity of [Fe/H] = -0.5 dex. Using these results on the metallicity bias of the Δa system we find the observational systems in use suitable to identify CP stars in other galaxies or distant regions of our own Galaxy and capable to provide data samples on a statistically meaningful basis. In turn, the synthetic system is suitable to test the performance of model atmospheres for CP stars. This work will be presented in follow-up papers of this series.

The Brightest Stars in Nearby Galaxies IX: Comparison of Ground-Based and HST Phtotmetry of the Brightest Stars in IC 4182

view Abstract Citations (7) References (36) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Brightest Stars in Nearby Galaxies IX: Comparison of Ground-Based and HST Photometry of the Brightest Stars in IC 4182 Sandage, Allan ; Carlson, George ; Kristian, Jerome ; Saha, Abhijit ; Labhardt, Lukas Abstract The distance to the Sdm dwarf galaxy IC 4182 is known from the measurements of its Cepheids made with the prerepair HST by Saha et al. [ApJ, 425,14(1994)]. IC 4182 is the parent galaxy of the type Ia supernova 1937C. Because of this it is important for calibrating the SNe Ia prime distance indicator as well as other secondary indicators. We compare HST photometry for the brightest stars in IC 4182 with two independent sets of Palomar ground-based data, one using the Argelander step-scale method tied to a photoelectric sequence; the other done with a CCD camera. Finding charts are given for all the stars that were measured. The three purposes of the study are (1) to test the photometric zero points used for the HST Cepheid measurements, (2) to obtain the magnitudes of the brightest blue and red stars in IC 4182 and to compare them with similar data in other galaxies that have Cepheid distances, and (3) to assess the effect of crowding on the brightest star problem by comparing the HST and the ground-based data where the angular resolutions differ by a factor of 10. For stars brighter than V = 22, the V band photometric zero points for the HST and the Palomar CCD data agree to within 0.05+/-0.03 mag, with an rms scatter of 0.16 mag. The I band zero points agree to within 0.02+/-0.04 mag, with an rms scatter of 0.14 mag. These confirm the magnitude zero points used in the HST Cepheid photometry in IC 4182. The mean apparent magnitudes of the three brightest blue stars are <B3> = 20.34, <V3> = 20.11, <R3> = 20.18, and <I3> = 20.12. The respective absolute magnitudes, using the Cepheid modulus of m-M = 28.36, are -8.02, -8.25, -8.18, and -8.24. The corresponding data for the brightest red stars are <B3> = 22.36, <V3> = 20.76, <R3> = 19.92, and <I3> = 18.94. The absolute magnitudes are -6.00, -7.60, -8.44, and -9.42. Problems of membership of the candidate stars are discussed. The absolute magnitudes in B and V fit well with similar data for the brightest stars in other galaxies, increasing confidence in such stars as secondary distance indicators. Publication: The Astronomical Journal Pub Date: May 1996 DOI: 10.1086/117925 Bibcode: 1996AJ....111.1872S Keywords: GALAXIES: STELLAR CONTENT; GALAXIES: INDIVIDUAL: IC4182 full text sources ADS | data products SIMBAD (6) NED (1) MAST (1) ESA (1) Related Materials (8) Part 1: 1976AJ.....81..743S Part 2: 1983AJ.....88.1569S Part 3: 1984AJ.....89..621S Part 4: 1984AJ.....89..630S Part 5: 1985AJ.....90.1019S Part 6: 1985AJ.....90.1464S Part 7: 1986AJ.....91..496S Part 8: 1988AJ.....96.1599S

Massive Star Populations in Nearby Galaxies

Massive stars are among the main drivers of the evolution of galaxies. These 0 type stars, along with their highly evolved descendants, the even more energetic Wolf-Rayet objects, are major contributors to the UV radiation and power the far-infrared luminosities through the heating of dust. Their stellar winds are important sources of mechanical power. As progenitors of supernovae, massive stars are agents of nucleosynthesis and may be intimately involved in the initiation of new star formation processes. Hence, massive star evolution is a key study in the exploration of the nearby and distant Universe. The laws of physics are, so far as we know, the same throughout the Uni­ verse. Why should we study massive stars in other galaxies, which is certainly more difficult than studying these objects nearby? We do so because the initial compositions of those stars, in particular their modes of star formation and environments, may well differ from place to place. This leads to different evolutionary histories with a number of observable consequences. For exam­ ple, it has been known for quite some time that the number ratio of blue to red supergiants shows a gradient in the Milky Way and seems to be different from the ratios found in the Magellanic Clouds. Also, the relative frequency of Wolf-Rayet (W-R) stars to their O-type progenitors appears to be much larger in inner Galactic regions compared to some low-metallicity galaxies. Similarly,

Massive Star Populations in Nearby Galaxies

Massive stars are among the main drivers of the evolution of galaxies. These 0 type stars, along with their highly evolved descendants, the even more energetic Wolf-Rayet objects, are major contributors to the UV radiation and power the far-infrared luminosities through the heating of dust. Their stellar winds are important sources of mechanical power. As progenitors of supernovae, massive stars are agents of nucleosynthesis and may be intimately involved in the initiation of new star formation processes. Hence, massive star evolution is a key study in the exploration of the nearby and distant Universe. The laws of physics are, so far as we know, the same throughout the Uni­ verse. Why should we study massive stars in other galaxies, which is certainly more difficult than studying these objects nearby? We do so because the initial compositions of those stars, in particular their modes of star formation and environments, may well differ from place to place. This leads to different evolutionary histories with a number of observable consequences. For exam­ ple, it has been known for quite some time that the number ratio of blue to red supergiants shows a gradient in the Milky Way and seems to be different from the ratios found in the Magellanic Clouds. Also, the relative frequency of Wolf-Rayet (W-R) stars to their O-type progenitors appears to be much larger in inner Galactic regions compared to some low-metallicity galaxies. Similarly,

First results from the Goddard High-Resolution Spectrograph - Spectroscopic determination of stellar parameters of Melnick 42, an O3f star in the Large Magellanic Cloud

view Abstract Citations (36) References (15) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS First Results from the Goddard High-Resolution Spectrograph: Spectroscopic Determination of Stellar Parameters of Melnick 42, an O3f Star in the Large Magellanic Cloud Heap, S. R. ; Altner, B. ; Ebbets, D. ; Hubeny, I. ; Hutchings, J. B. ; Kudritzki, R. P. ; Voels, S. A. ; Haser, S. ; Pauldrach, A. ; Puls, J. ; Butler, K. Abstract GHRS and optical (ESO 3.6 m) observations of the O3f star Melnick 42 in the 30 Doradus complex are reported. A first analysis reveals that with a luminosity of 2.3 x 10^6^ L_sun_ and a present mass of 100 M_sun_, Melnick 42 is one of the most luminous and massive stars known. An estimate of abundances indicates that iron and oxygen are very likely reduced by a factor of 4 relative to the Sun, whereas carbon is more strongly depleted and nitrogen is approximately solar. The terminal velocity of the stellar wind is 3000 km s^-1^. The mass-loss rate is 4 x 10^-6^ M_sun_ yr^-1^, with a large uncertainty. The excellent quality GHRS spectrum taken in a crowded region of the LMC demonstrates the superiority of the HST for quantitative ultraviolet spectroscopy of hot stars in other galaxies. Publication: The Astrophysical Journal Pub Date: August 1991 DOI: 10.1086/186109 Bibcode: 1991ApJ...377L..29H Keywords: Hubble Space Telescope; O Stars; Spectrographs; Supermassive Stars; Ultraviolet Spectroscopy; Visible Spectrum; High Resolution; Hot Stars; Magellanic Clouds; Stellar Mass Ejection; Stellar Winds; Astrophysics; GALAXIES: MAGELLANIC CLOUDS; STARS: INDIVIDUAL NAME: MELNICK 42; STARS: MASSIVE; STARS: OF-TYPE; STARS: WINDS; ULTRAVIOLET: SPECTRA full text sources ADS | data products SIMBAD (2) NED (1) MAST (1) ESA (1)

Wolf-Rayet Stars

The properties and evolutionary status of WR stars are examined, reviewing the results of recent observational and theoretical investigations. Topics discussed include spectral types and line strengths, magnitudes and colors, intrinsic variability, IR and radio observations, X-ray observations, the Galactic distribution of WR stars, WR stars in other galaxies, and WR binaries. Consideration is given to the inferred masses, composition, and stellar winds of WR stars; model atmospheres; WR stars and the Galactic environment; and WR stars as a phase of stellar evolution. Diagrams, graphs, and tables of numerical data are provided.

Further candidates of supermassive stars in other galaxies

To look for other supermassive stars in other galaxies means to answer the question: what is the spectroscopic and morphological signature of such objects? The interpretation of WR sources found in other supergiant HII complexes depends basically on our picture of 30 Dor and in particular of R136a.

Studies of luminous stars in nearby galaxies. I. Supergiants and O stars in the Milky Way.

In this paper the fundamental properties of the brightest known stars in our Galaxy are determined for future comparison with results for the most luminous stars in other galaxies. The H-R diagrams (M/sub v/ versus spectral type and M/sub bol/ versus log T/sub e/), the luminosities of the brightest stars, and the ratios of blue to red supergiants are all discussed, and a catalog of over 1000 supergiants and O stars in associations and clusters is included at the end of the paper.The ''theoretical'' H-R diagram (M/sub bol/ versus log T/sub e/) reveals a group of superluminous O stars with M/sub bol/ between -12 mag, a lack of evolved supergiants at these very high luminosities, and an apparent upper limit to the luminosities of the later-type supergiants (>B5) near M/sub bol/=-9.5 mag.The most luminous red supergiants have a maximum visual luminosity near M/sub v/approx. =-8 mag, supporting the suggestion by Sandage and Tammann that they are good distance indicators. Excluding the superluminous star Cyg OB 2 No. 12 (M/sub v/approx. =-9.9 mag), the brightest blue stars are found at M/sub v/approx. =-8.5 mag.The variation of the ratio of blue to red supergiants with luminosity is discussed. There is also evidencemore » for a gradient in this ratio with distance from the galactic center, although the results are limited by the incompleteness of the data.« less

The HR Diagram for Luminous Stars in Nearby Galaxies

HR diagrams for the stellar populations in other galaxies play a fundamental role in our understanding of the progress of stellar evolution and the effects of possible variations in chemical composition. It is important to compare what little information we have about stars in other galaxies with the same types of stars in our own Milky Way. Basically we are asking - are they the same, and how universal are the processes we observe in our Galaxy?

Luminosities of LMC OB Stars

Our knowledge of the spectra of stars in other galaxies is essentially limited to those which are extremely luminous. In the LMC, slit spectra of ~ 200 stars have been obtained (Feast, Thackeray and Wesselink 1960, Ardeberget al. 1972) down toUsing an objective prism technique, Brunetet al. (1975) have been able to detect 272 OB stars within the LMC. At the fainter limit this survey should include relatively normal 0 and early B dwarfs and giants. The principal aim of the present investigation was to obtain spectra of these stars for comparison with galactic stars and to apply the techniques of MK classification and measurement of Hγ equivalent widths to determine their luminosities and hence a distance modulus to the LMC.

WHAT STARS BECOME SUPERNOVAE?

ABSTRACT This paper assembles a variety of empirical lines of evidence on the masses and stellar-population types of stars that trigger supernova (SN) explosions. The main theoretical motivations are to determine whether type I supernovae (SN I) can have massive precursors and whether there is an interval of stellar mass between the masses of precursors of pulsars and white dwarfs that is disrupted by carbon detonation. Statistics of stellar birthrates, SN, pulsars, and SN remnants in the Galaxy show that SN II (or all SN) could arise from stars with masses greater than about 12 to 49 solar masses. Several methods of estimating the masses of stars that become white dwarfs are consistent with a lower limit of about 5 solar masses, so carbon detonation may be avoided. Studies of the properties of galaxies in which SN occur, and their distributions within galaxies, support the usual views that SN I have low-mass precursors and SN II have massive precursors. The restriction of known SN II to Sc and Sb galaxies is shown to be statistically consistent with massive stars in other galaxies also dying as SN II. Possible implications of the peculiarities of some SN-producing galaxies are discussed.