Physical parameters of pre-main sequence stars in open clusters

Abstract

Aims. The aims are twofold: we search and analyse pre-main sequence (PMS) stars in Galactic young open clusters (YOCs) to determine the ages, masses, and spatial distribution of PMS members in YOCs, and to check and compare the performances of different model isochrones. Methods. We compare UBVRI photometric observations to theoretical isochrones in the photometric diagrams. The comparison simultaneously provides membership assignments for both main sequence (MS) and PMS stars and estimates for the physical properties of the cluster candidate members: masses, ages, and spatial distribution inside the cluster. Results. The photometric measurement of an average (U − V) excess, supposedly indicative of accretion disks, is considered prior to membership assignment. This photometric excess is correlated with cluster age, suggesting that disks able to show up in (U − V) excess vanish at ages around 5 Myr. We find that comparing photometry to models in the colour-magnitude (CM) diagram leads to better results for the masses than performing the comparison in the theoretical HR plane. The obtained cluster mass functions show a marginal steepening with cluster age. Significant variations in the mass function slopes are found with the models used in member selection. The clusters NGC 3293 and NGC 2362 are found to have mass functions flatter than the Salpeter slope for all models considered. The relation between the calculated dispersion of PMS age and the characteristic clustering scale of the cluster shows interesting agreement with previous findings in star-forming regions in a wide range of scales. Finally, the ratio of characteristic clustering scales for PMS candidate members in different mass ranges can be interpreted as suggesting mass segregation, in the sense of a relatively wider spatial distribution for the lower mass members in older clusters. Conclusions. The relations between the different cluster parameters show that the procedure applied to assign cluster membership and to measure physical parameters for the selected members is well founded.

Chandra X-ray observation of the young stellar cluster NGC 3293 in the Carina Nebula Complex

“…They argue that NGC 3293 is the cluster with the most convincing evidence for a strong deficit of low-mass stars. Delgado et al (2011) also arrived at a similar conclusion from their optical photometry study, which suggested that the mass function is considerably flatter than the Salpeter slope below 2.5 M .…”

“…This will also provide an important clarification about the previous claims of a significant deficit of low-mass stars in NGC 3293 that were made in some optical photometric studies (Slawson et al 2007;Delgado et al 2011). Our aim here is to determine the number of stars in the [1 − 2] M mass range.…”

“…The presence of evolved massive stars, main-sequence stars up to spectral type B0.5 V, and comparisons of optical color magnitude diagrams with stellar evolution models suggested an age of ≈ 8 − 10 Myr for the high-mass population in this cluster (Slawson et al 2007;Delgado et al 2011).…”

B fields in OB stars (BOB): Detection of a magnetic field in the He-strong star CPD −57° 3509

“…The observed Johnson V magnitude and B − V colour are adopted from Delgado et al (2011). The colour excess E(B − V) was determined by comparison with synthetic photometry from the Atlas9 flux.…”

TheGaia-ESO Survey: pre-main-sequence stars in the young open cluster NGC 3293

“…The procedure for member selection has been described and applied to a sample of 11 southern clusters by Delgado et al (2007Delgado et al ( , 2011hereafter DAYI, DAYII). A spectroscopic assessment of this method for selecting photometric candidate members is now possible for NGC 3293, the only cluster in our sample which is also included in the observations of the Gaia-ESO Spectroscopic Survey (GES).…”