Three stellar associations and their field east of LMC 4 in the Large Magellanic Cloud

Abstract

Abstract. We present BVR photometry in an area of 20. 5 × 20. 5 centered on LH 95 situated to the north-east of the super-bubble LMC 4. We investigate the stellar content of three stellar associations (LH 91, and their surrounding fields. Our observations use the R−Hα colour index to identify the Be star population of the region. We find that Be stars exist in all three of the investigated associations. Within LH 95 we find a central cluster of four Be stars which strongly determine the Hii emissivity in this area. We estimated the reddening and the age of the systems based on isochrone fitting. The reddening was found to vary between E(B − V ) 0.15 and 0.20 mag. All systems were found to be younger than 10 Myr, while the field is older than ∼50 Myr. We also present the luminosity and mass functions of the systems, as well as that of the field. It was found that the luminosity function slope s of the field is steeper than that of the systems, which were found to be s 0.12-0.32. The MF slopes were estimated for both systems and field by directly counting stars between evolutionary tracks. We verify that the MF slopes of the systems are rather shallower than the ones of the field. The MF slopes of the systems lie in the range −1.0 < Γ < −2.0, while those of various fields are significantly steeper, around Γ −4.0. LH 95 was found to be probably under disruption. We discuss the possibility that this association is in the process of dissipation.

The Low‐Mass Initial Mass Function of the Field Population in the Large Magellanic Cloud withHubble Space TelescopeWFPC2 Observations

“…However, Massey & Hunter (1998) found that the IMF slope in R136 in 30 Doradus is indistinguishable from those of Galactic and Magellanic Cloud OB associations and they suggest that star formation produces the same distribution of masses over a range of $200 times in stellar density, from that of sparse OB associations to that typical of globular clusters. Indeed the IMF slopes of LMC associations as found by various authors (Massey et al 1989a(Massey et al , 1989bParker et al 1992;Garmany et al 1994;Oey & Massey 1995;Oey 1996;Dolphin & Hunter 1998;Parker et al 2001;Olsen et al 2001;Gouliermis et al 2002) are similar, considering the observational constraints, and are clustered around À % À1:5 AE 0:1 for intermediate-to high-mass stars. This slope is not very different from the mass function slopes of typical LMC clusters for the same mass range (e.g., Hunter et al 1997;Fischer et al 1998;Grebel & Chu 2000;de Grijs et al 2002ade Grijs et al , 2002bGouliermis et al 2004).…”

“…An example of such a process has been presented by Gouliermis et al (2002), who found a clear difference between the IMF slope of association LH 95 in the LMC, its surrounding field and the general field of the galaxy for the same mass range (3 P M/M P 10), with the IMF becoming gradually steeper outward from the main body of the association. They interpret this phenomenon as due to the evaporation of the dispersed association, which feeds the general LMC field with intermediatemass stars through its surrounding field, while the system itself is characterized by a centrally concentrated clump of massive stars, as if mass segregation takes place.…”

Discovery of the Pre-Main-Sequence Population of the Stellar Association LH 95 in the Large Magellanic Cloud with Hubble Space Telescope Advanced Camera for Surveys Observations

“…There is a bright cutoff in the CMD of the field (Fig. 2, middle) because of the lack of short exposures, but previous groundbased photometry by Gouliermis et al (2002) has shown that this area does not include any UMS stars. On the other hand, a pronounced turnoff at around mag and a red giant V Ӎ 22.5 branch (RGB) with its red clump clearly located at around and mag, typical of the LMC field (e.g., V Ӎ 19 V Ϫ I Ӎ 1.2 Elson et al 1997;Smecker-Hane et al 2002), can be seen in both CMDs.…”

Hierarchical star formation across the grand-design spiral NGC 1566

“…For example, the IMF of field massive stars is found to be much steeper than that of star-forming clusters and associations in the Magellanic Clouds (Massey 2003, and references therein). In general, star-forming systems have a preference to top-heavy MFs, while the field shows mostly bottom-heavy MFs (e.g., Gouliermis et al 2002). The variation of integrated galactic MF slopes from bottom-to top-heavy has been explained by the differences in galaxy-wide star formation rates (e.g., Weidner et al 2010;Kroupa 2014), as the areal SFR inside the young stellar systems is higher than away from them.…”