Stellar contents and Star Formation in IRAS 18456-0223

Abstract

We use various analytical techniques to study Young Stellar Objects (YSOs) in an area of approximately $10' \times 10'$ in the IRAS 18456-0223 star-forming region. We use archival optical (Gaia DR3) and infrared (2MASS, UKIDSS, Spitzer, WISE, and Herschel) data, along with our optical spectroscopy of three bright stars for this purpose. We identify 89 YSOs (80 Class II and 9 Class I) based on their infrared properties. Our multiwavelength SED fits of selected YSOs show that they have masses $\sim 0.1$--$7.2$ $M_\odot$ and are up to $4$ Myr old. Our Minimum Spanning Tree (MST) analysis shows that these YSOs, situated at around 600 pc, form clusters with radial extents of order 0.5 pc and mean surface densities of $\sim 60$ pc$^{-2}$. We compare UKIDSS and 2MASS data of the YSOs and find that some of them show variability. We construct maps based on Herschel data which reveal multiple column density peaks ($N_{\rm H_2} \sim 10^{22}$ cm$^{-2}$) embedded in cold ($T_d \sim 10$--$13$ K) filaments. Our near-infrared extinction map exhibits several high-$A_V$ peaks, some of which coincide with the sub-mm column density maxima. Using our optical spectra of three bright sources, we show that they are of A--K spectral type. One star shows the Li I 6707 Å line, indicating its youth.

Figures (16)

• Figure 1: (a) MIR CCD using the procedure outlined in 2009ApJS..184...18G. class I and class II are highlighted in red and blue, respectively. (b) NIR–MIR CCD using the procedure of 2009ApJS..184...18G. The regions of class I and class II sources have been labelled. (c) NIR CCD in the CIT system. The red, blue curve, and green line show the giant locus, dwarf locus 1988PASP..100.1134B, and the CTTS locus 1997AJ....114..288M, respectively. Three parallel slanted dashed lines mark the reddening vectors, drawn using the extinction law of 1981ApJ...249..481C. The reddening lines extending from the tip of the giant branch to the base of the main-sequence dwarf locus delineate the main-sequence reddening band. Sources located within the region labeled 'F' are likely field stars or evolved cluster members with little or no near-infrared excess. The sources in 'T' and 'P' regions are taken to be class II and class I sources respectively. However, we there may be overlap of the Herbig Ae/Be stars in the “T” region hillenbrand2002youngcircumstellardisksevolution.(d) NIR-MIR CCD by 2014ApJ...791..131K
• Figure 2: Left panel: Proper motion vector-point diagrams (VPDs; top subpanels) and Gaia DR3$G$ vs. $(G_\mathrm{BP} - G_\mathrm{RP})$ colour–magnitude diagrams (CMDs; bottom subpanels) for stars in the IRAS 18456-0223 region. The leftmost subpanels show all stars, while the middle and right subpanels display the high-probability cluster members and field stars, respectively. Right panel: Proper motion uncertainties ($\sigma_\mathrm{PM}$) and parallaxes plotted as a function of $G$ magnitude. High-probability members with $P_\mu > 50\%$ are indicated by green triangles.
• Figure 3: Histogram of parallax values for cluster members, with a Gaussian profile overlaid. The best-fit Gaussian has a mean parallax of $1.649 \pm 0.325$ mas. Only sources with positive parallaxes were considered, and the fit was restricted to the range $0.5 < \varpi < 3$ mas to exclude outliers.
• Figure 4: Proper motion versus distance for Gaia DR3 YSO candidates. Triangles denote $\mu_{\alpha}$ and circles denote $\mu_{\delta}$, with error bars representing uncertainties in both distance and proper motion. Dashed lines indicate the combined medians for the green sources, and overlaid error ellipses (2$\times$MAD in a darker shade and 3$\times$MAD in a lighter shade) illustrate the dispersion.
• Figure 5: Proper Motion Plot for the YSOs (green and red sources taken, green arrows) overlaid in Ks band Image obtained from the 2MASS Interactive Image Service at IRSA. The distribution of YSOs based on their class is also depicted where red sources are class II while blue sources are class I. Yellow-marked sources were successfully fitted using SED models.