A [ITAL]Hubble[/ITAL] [ITAL]Space[/ITAL] [ITAL]T[/ITAL][ITAL]elescope[/ITAL] Study of Extragalactic OB Associations

Bresolin, Fabio; Kennicutt, Robert C.; Ferrarese, Laura; Gibson, Brad K.; Graham, J. A.; Macri, Lucas M.; Phelps, Randy L.; Rawson, Daya M.; Sakai, Shoko; Silbermann, N. A.; Stetson, P. B.; Turner, Anne Marie Stewart

doi:10.1086/300424

Cited by 53 publications

(43 citation statements)

References 28 publications

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“…D S = 6 is similar to the values derived by Borissova et al (IC 1613, 6.6 ) and Pietrzynski et al (NGC 300, 7.7 ), and much larger than those adopted by Bresolin et al (1996Bresolin et al ( , 199883 to 3.9 in different spiral galaxies at ∼10 Mpc). Since Borissova et al, Pietrzynski et al and this work used 2m-class ground-based telescopes with comparable instrumentation, whereas Bresolin et al used HST-WFPC2 data, it is tempting to interpret the differences in terms of the superior plate scale of the WFPC2 (0.1 /px) breaking the OB associations into smaller pieces.…”

Section: Free Parameters Of the Codesupporting

confidence: 89%

The young stellar population of IC 1613

García¹,

Herrero

Vicente³

et al. 2009

A&A

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Context. 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. Aims. In preparation for the new instrumentation planned for the Gran Telescopio CANARIAS (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. Methods. 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 friendsof-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. Results. 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.

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Section: Free Parameters Of the Codesupporting

confidence: 89%

The young stellar population of IC 1613

García¹,

Herrero

Vicente³

et al. 2009

A&A

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“…Ivanov (1996) found an average size of roughly 80 pc from the average of an heterogenous set of data including IC 1613, other irregular galaxies (NGC 6822, Pegasus, Sextans A, GR 8, Ho IX) and nearby spirals (M 31, M 33). Bresolin et al (1998) analyzed HST-WFPC2 data for 7 spirals, and found the same value. Bresolin et al (1996) finds very similar association size distributions in LMC, SMC, M 33, NGC 6822, and M 101, with a peak in the range 40-80 pc and a mean size of 90 pc.…”

Section: Comments On Individual Associationsmentioning

confidence: 63%

“…Substructure had already been found in early catalogs of associations made by eye (Blaauw 1964), but also by Bresolin et al (1998) and Pietrzyński et al (2001Pietrzyński et al ( , 2005, who both find that associations larger than 200 pc can be separated into smaller denser groups. We only find one association of roughly 200 pc in diameter, #151, and visual inspection indeed reveals that it could be broken into smaller pieces of high density.…”

Section: Sizementioning

confidence: 82%

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The young stellar population of IC 1613

García

Herrero

Castro

et al. 2010

A&A

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Context. To understand the structure and evolution of massive stars, systematic surveys of the Local Group galaxies have been undertaken, to find these objects in environments of different chemical abundances. We focus on the metal-poor irregular galaxy IC 1613 to analyze the stellar and wind structure of its low-metallicity massive stars. We ultimately aim to study the metallicitydependent driving mechanism of the winds of blue massive stars and use metal-poor massive stars of the Local Volume as a proxy for the stars in the early Universe. Aims. In a previous paper we produced a list of OB associations in IC 1613. Their properties are not only a powerful aid towards finding the most interesting candidate massive stars, but also reveal the structure and recent star formation history of the galaxy. We characterize these OB associations and study their connection with the galactic global properties. Methods. The reddening-free Q parameter is a powerful tool in the photometric analysis of young populations of massive stars, since it exhibits a smaller degree of degeneracy with OB spectral types than the B − V color. The color-magnitude diagram (Q vs. V) of the OB associations in IC 1613 is studied to determine their age and mass, and confirm the population of young massive stars. Results. We identified more than 10 stars with M ≥ 50 M . Spectral classification available for some of them confirm their massive nature, yet we find the common discrepancy with the spectroscopically derived masses. There is a general increasing trend of the mass of the most massive member with the number of members of each association, but not with the stellar density. The average diameter of the associations of this catalog is 40 pc, half the historically considered typical size of OB associations. Size increases with the association population. The distribution of the groups strongly correlates with that of neutral and ionized hydrogen. We find the largest dispersion of association ages in the bubble region of the galaxy where hydrogen is abundant, implying that recent star formation has proceeded over a longer period of time than in the rest of the galaxy, and is still ongoing. Very young associations are found at the west of the galaxy far from the bubble region, traditionally considered the sole locus of star formation, but still rich in neutral hydrogen. Conclusions. The contrast in the stellar properties derived from photometry and spectroscopy (when the latter is available) shows that the Q pseudo-color is very useful for estimating the parameters of OB stars when only photometric observations exist. This work helped define an extensive pool of candidate OB stars for subsequent spectroscopic analyses designed to study the structure and winds of metal-poor massive stars.

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“…The final number of bright main sequence stars selected for this investigation in each galaxy are listed in Table 2. The value of V − I < 0.23 was selected as in Bresolin et al (1998) who studied the same galaxies. We tested different values of V − I, which were lower and higher than the one selected.…”

Section: Observational Datamentioning

confidence: 99%

Star forming regions in a sample of HST spiral galaxies

Drazinos

Kontizas

Karampelas

et al. 2013

A&A

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Aims. The presence of small-and large-scale star formation structures in a sample of six spiral Hubble Space Telescope (HST) galaxies is investigated to identify small structures of young stars known as OB associations and to tell whether they are formed inside larger scale star forming stellar structures in a hierarchical form. Methods. This process was based on a friend-of-friend (FOF) algorithm applied to the bright, early type stars above a certain color cutoff limit in order to ensure that we include main sequence stars. A size criterion was introduced in order to apply the same algorithm to different types of stellar structures. Depending on their size, the structures were divided into the four categories of associations, aggregates, complexes, and supercomplexes. Results. Star forming structures of the four types mentioned above are found in all six galaxies of our sample. The majority of the associations and aggregates (the smaller structures) found are lying inside larger structures like complexes and supercomplexes, indicating a hierarchical star formation mechanism.

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A [ITAL]Hubble[/ITAL] [ITAL]Space[/ITAL] [ITAL]T[/ITAL][ITAL]elescope[/ITAL] Study of Extragalactic OB Associations

Cited by 53 publications

References 28 publications

The young stellar population of IC 1613

The young stellar population of IC 1613

The young stellar population of IC 1613

Star forming regions in a sample of HST spiral galaxies

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