Characterizing the Low-Mass Pre-Main-Sequence Population in the Low-Metallicity Star-Forming Region Dolidze 25 Using VLT-MUSE

TL;DR

This study investigates how low metallicity affects the formation and accretion of low-mass pre-main-sequence stars in the metal-poor cluster Dolidze 25 using VLT-MUSE optical spectroscopy. By combining Gaia astrometry, Li I absorption, and Balmer emission as youth diagnostics, the authors identify 132 cluster members, with 95 classified as PMS, and derive Teff, Av, L, and masses using low-metallicity BT-Settl models. Mass accretion rates span from 10^-10 to 10^-8 solar masses per year (median ~8×10^-10), consistent with solar-metallicity regions and suggesting minimal metallicity dependence in accretion for these masses and ages. They show that solar-metallicity templates bias Teff and Av high, highlighting the need for metallicity-matched models in metal-poor environments, and provide flux-calibrated spectra to aid future disk-evolution studies in subsolar regimes. Overall, the work demonstrates that metallicity alone does not dominate PMS accretion behavior and showcases MUSE's capability to probe distant, metal-poor star-forming regions.

Abstract

The metallicity of the star-forming environment is a fundamental parameter shaping the evolution of protoplanetary disks and the formation of planetary systems, yet its influence remains poorly constrained. We present a spectroscopic study of low-mass pre-main sequence (PMS) stars ($M < 1 \, M_\odot$) in the exceptionally metal-poor cluster Dolidze~25 ($Z \approx 0.2 \, Z_\odot$), using VLT/MUSE observations to probe accretion processes and disk evolution in a subsolar environment. We identify 132 cluster members using a combination of \textit{Gaia} astrometry and spectroscopic youth indicators, including lithium absorption and Balmer emission. The stellar parameters are derived using low-metallicity BT-Settl models yielding effective temperatures, extinctions, luminosities enabling robust estimates of stellar masses and ages. Mass accretion rates ($\dot{M}_\mathrm{acc}$) derived from H$α$ emission span $10^{-10}$--$10^{-8} \, M_\odot\,\mathrm{yr}^{-1}$ with a median value of \(8 \times 10^{-10}\,M_\odot\,\mathrm{yr}^{-1}\). These rates are comparable to those in solar-metallicity regions of similar age, such as Lupus and Orion, indicating minimal metallicity dependence in accretion processes. Our analysis shows that using solar-metallicity templates to fit low-metallicity stars leads to systematic overestimations of \(T_\mathrm{eff}\) (by approximately \(300\,\mathrm{K}\)) and \(A_V\) (by around \(0.5\,\mathrm{mag}\)), underscoring the importance of employing metallicity-matched models for reliable characterization in low-\(Z\) environments. We present flux-calibrated, extinction-corrected spectra of these metal-poor PMS stars as a valuable resource for future investigations of disk evolution in subsolar regimes.

Figures (21)

• Figure 1: RGB image of Dolidze 25 created from the $r$-, $i$-, and $z$-band images generated by integrating the MUSE datacube over the corresponding Pan-STARRS filter wavelength ranges. Two pointings were obtained toward the cluster core, centered at (06h45m0268, +0013114) for Field C (left) and (06h44m5882, +0013114) for Field D (right), covering the central $2'\times1'$ region of the cluster.
• Figure 2: Left: Sample spectrum without sky subtraction, processed with ESORex, showing telluric and nebular contamination from a background region. Middle: Spectrum of a point source from MUSEpack-reduced cube with telluric absorption removed while retaining the nebular emission background. Right: Final spectrum after subtracting both telluric and nebular emission, revealing the intrinsic spectrum of the point source.
• Figure 3: Left: Comparison of synthetic photometry from MUSE with Pan-STARRS , where the residual is defined as Pan-STARRS $-$ Synthetic Photometry. The median residual values are calculated from a sample of 30 sources, with Pan-STARRS $i$ magnitudes brighter than 19 and $r$ magnitudes brighter than 20. Right: Comparison of MUSE spectra for the brightest source in the field of view with high-resolution VLT-UVES spectra, showing consistent flux calibration between the two.
• Figure 4: Proper motion in Right Ascension (pmRA) versus Declination (pmDec) for sources within a 3$\arcmin$ radius of Dolidze 25. Red points represent cluster members identified by DBSCAN; gray points indicate outliers.
• Figure 5: Comparison of observed optical spectra (blue) of Cl* Dolidze 25 MV 15 (O7 V) and Cl* Dolidze 25 MV 18 (B0.5–1 V) with synthetic spectra from PoWR models at three different metallicities: solar ($Z/Z_\odot = 1.0$, black), LMC ($Z/Z_\odot = 0.5$, green), and SMC ($Z/Z_\odot = 0.2$, red). Key diagnostic lines, including He, CNO, and Si, are marked. The observed weakness of metal lines relative to the solar model indicates a subsolar metallicity.