Stellar contents and star formation in the NGC 7538 region

Abstract

Deep optical photometric data on the NGC 7538 region were collected and combined with archival data sets from Chandra, 2MASS and Spitzer surveys in order to generate a new catalog of young stellar objects (YSOs) including those not showing IR excess emission. This new catalog is complete down to 0.8 M ⊙ . The nature of the YSOs associated with the NGC 7538 region and their spatial distribution are used to study the star formation process and the resultant mass function (MF) in the region. Out of the 419 YSOs, ∼91% have ages between 0.1 to 2.5 Myr and ∼86% have masses between 0.5 to 3.5 M ⊙ , as derived by spectral energy distribution fitting analysis. Around 24%, 62% and 2% of these YSOs are classified to be the Class I, Class II and Class III sources, respectively. The X-ray activity in the Class I, Class II and Class III objects is not significantly different from each other. This result implies that the enhanced X-ray surface flux due to the increase in the rotation rate may be compensated by the decrease in the stellar surface area during the pre-main sequence evolution. Our analysis shows that the O3V type high mass star 'IRS 6' might have triggered the formation of young low mass stars up to a radial distance of 3 pc. The MF shows a turn-off at around 1.5 M ⊙ and the value of its slope 'Γ' in the mass range 1.5 <M/M ⊙ < 6 comes out to be −1.76 ± 0.24, which is steeper than the Salpeter value.

Search for variable stars in the young open cluster Stock 18

“…From the SED fitting analyses (for details, cf. [7]), the average age and mass of probable PMS-variables come out to be 2.7 ± 0.3 Myrs and 2.7 ± 0.2 M , respectively which suggests that these stars should be T Tauri stars. Disk/envelope accretion rates and masses of these PMS variable stars are also determined from the SED fitting and detailed analyses is underway.…”

“…The evolutionary status of these variables was explored through their position in the HertzsprungRussell diagram (for details, see [7]). Out of the detected variables, 168 have good photometric data (error < 0.1) and 80 of them have ages > 10 Myr.…”

Stellar Cores in the Sh 2-305 H ii Region

“…This method has been extensively used in our previous studies (see. e.g., Jose et al 2016;Sharma et al 2017, and references therein). We constructed the SEDs of the YSOs using the multiwavelength data (optical to MIR wavelengths, i.e.…”

Variable stars in the Sh 2-170 H ii region

“…The individual age and mass of each PMS variables can be determined from their position in the CMD by using the procedure discussed by Chauhan et al (2009) and Sharma et al (2017). The estimated age and mass of the PMS variables and the YSOs are given in Table 3 and Table 4, respectively.…”

“…This method has been extensively used in our previous studies (see. e.g., Jose et al 2016;Sharma et al 2017, and references therein). We were able to construct SEDs for the 43 PMS variables using the available optical, NIR (2MASS) and MIR (WISE, Spitzer) data, with a condition that each star should have photometric data at least in five bands.…”