Star complexes and associations in the Andromeda galaxy

Efremov, Yu. N.; Ivanov, G. R.; Nikolov, Nikola S.

doi:10.1007/bf00644467

Cited by 43 publications

(45 citation statements)

References 9 publications

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“…At the distance of 2600 pc adopted for the association, it would have a linear size of 270 pc in diameter. This size is consistent with the typical sizes traditionally accepted for the stellar association (Efremov et al 1987).…”

Section: Size and Agesupporting

confidence: 91%

Members of Centaurus OB1 and NGC 4755: new spectroscopic and astrometric studies

Corti

Orellana

2013

A&A

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Context. An OB association is a gravitationally unbound group of stars. The identification of the members of the association is an important aspect of its study. There are few astrometric membership studies for OB associations, but the combination of these studies with astrophysical techniques becomes a very powerful tool for this type of research. Aims. We perform new spectroscopic and astrometric studies of the members of the association Centaurus OB1 (Cen OB1) and the open cluster NGC 4755. Methods. To carry out this study we used new spectroscopic optical observations obtained at CASLEO, and proper motion and photometric data from the Tycho-2 Catalogue and other databases available via the Internet.Results. With this investigation we found 52 members of Cen OB1 (l = 303.• 7, b = 0.• 4) and four members of NGC 4755 (l = 303.• 2, b = 2.• 5), an open cluster integrated into the Cen OB1 stellar association. The distance, heliocentric radial velocity, proper motion, and age of Cen OB1 are 2.6 ± 0.5 kpc, ∼−20 km s −1 , μ α cos δ = −4.78 ± 0.10 mas yr −1 , μ δ = −0.93 ± 0.10 mas yr −1 , and ∼20 × 10 6 years old, respectively. The same parameters found for NGC 4755 are 1.9 ± 0.5 kpc, −18 ± 2 km s −1 , μ α cos δ = −4.14 ± 0.19 mas yr −1 , μ δ = −1.09 ± 0.12 mas yr −1 , and ∼15 × 10 6 years old. The pulsars PSR J1253−5820 and PSR J1254−6150 could have been born as the result of supernovae explosions that occurred in the past by massive members of Cen OB1. We have seen Infrared Astronomical Satellite (IRAS) sources near Cen OB1, that show that star formation is still occurring. The age gradient observed between the different members of Cen OB1 makes it likely that the stellar association and IRAS sources represent different stages of a sequential formation process.

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Section: Size and Agesupporting

confidence: 91%

Members of Centaurus OB1 and NGC 4755: new spectroscopic and astrometric studies

Corti

Orellana

2013

A&A

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“…The sizes of complexes on the left wing of the distribution of Fig. 7 are comparable to those of typical stellar associations and aggregates in Local Group galaxies (e.g., Efremov et al 1987;Ivanov 1996). The Gaussian fit in Fig.…”

Section: Size Distributionsupporting

confidence: 63%

Hierarchical star formation across the grand-design spiral NGC 1566

Gouliermis

Elmegreen²,

Elmegreen

et al. 2017

Monthly Notices of the Royal Astronomical Society

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We investigate how star formation is spatially organized in the grand-design spiral NGC 1566 from deep HST photometry with the Legacy ExtraGalactic UV Survey (LEGUS). Our contour-based clustering analysis reveals 890 distinct stellar conglomerations at various levels of significance. These star-forming complexes are organized in a hierarchical fashion with the larger congregations consisting of smaller structures, which themselves fragment into even smaller and more compact stellar groupings. Their size distribution, covering a wide range in length-scales, shows a power-law as expected from scale-free processes. We explain this shape with a simple "fragmentation and enrichment" model. The hierarchical morphology of the complexes is confirmed by their mass-size relation which can be represented by a powerlaw with a fractional exponent, analogous to that determined for fractal molecular clouds. The surface stellar density distribution of the complexes shows a log-normal shape similar to that for supersonic non-gravitating turbulent gas. Between 50 and 65 per cent of the recentlyformed stars, as well as about 90 per cent of the young star clusters, are found inside the stellar complexes, located along the spiral arms. We find an age-difference between young stars inside the complexes and those in their direct vicinity in the arms of at least 10 Myr. This timescale may relate to the minimum time for stellar evaporation, although we cannot exclude the in situ formation of stars. As expected, star formation preferentially occurs in spiral arms. Our findings reveal turbulent-driven hierarchical star formation along the arms of a grand-design galaxy.

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“…We divided the stellar structures into the four main types introduced by Efremov (1987), associations (from 30 to 100 pc in size), aggregates (from 100 to 300 pc), complexes (from 300 to 1000 pc), and supercomplexes (from 1000 pc and above), so the code produces four graphs, one for each category (Fig. 5).…”

Section: Description Of Our Methodsmentioning

confidence: 99%

“…For M31 van den Bergh (1964) identified groups of blue stars with average size ∼500 pc. Efremov et al (1987) identified star complexes ∼600 pc average size. Magnier et al (1993) found a large number of groups with sizes from 50-150, roughly the average values of associations and aggregates in our study, and a few larger structures ∼400 pc in size.…”

Section: Comparison With Previous Investigationsmentioning

confidence: 99%

“…His method, the path linkage criterion, provided an objective tool to the identification process. Efremov (1987) categorized star forming regions into associations, aggregates, complexes and supercomplexes based on their size (Maragoudaki et al 1998;Livanou et al 2007). In this paper the division of the previous studies is adopted, therefor the size of associations is considered to be from 30 pc to 100 pc.…”

Section: Introductionmentioning

confidence: 99%

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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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Star complexes and associations in the Andromeda galaxy

Cited by 43 publications

References 9 publications

Members of Centaurus OB1 and NGC 4755: new spectroscopic and astrometric studies

Members of Centaurus OB1 and NGC 4755: new spectroscopic and astrometric studies

Hierarchical star formation across the grand-design spiral NGC 1566

Star forming regions in a sample of HST spiral galaxies

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