[Paper Review] XMM-Newton observation of the young open cluster Blanco 1. I. X-ray spectroscopy and photometry

I. Pillitteri, G. Micela+3 more|ArXiv.org|Mar 12, 2004

Stellar, planetary, and galactic studies23 references11 citations

TL;DR

This study presents the first X-ray spectroscopy and photometry of the young open cluster Blanco 1 using XMM-Newton data, detecting 190 X-ray sources with 88% completeness for cluster members. A two-temperature plasma model (0.3 keV and 1 keV) best fits the quiescent X-ray spectra of active stars, indicating coronal emission consistent with other young clusters like the Pleiades.

ABSTRACT

We present an X-ray study of the high metallicity young open cluster Blanco 1 based on XMM--Newton data. X-ray spectroscopy of cluster members is presented for the first time as well as new X-ray distribution functions of late-type stars. We detected all known dF and dG stars in the EPIC field and 80% and 90% of dK and dM stars, respectively. The X-ray spectral analysis of the X-ray brightest cluster stars and X-ray color analysis of a larger sample show that a model with two temperatures (at about 0.3 and 1 keV) explains the quiescent activity phase spectra. We discuss also the nature of unidentified X-ray sources in the observed region and their X-ray spectral properties.

Motivation & Objective

• To perform the first X-ray spectroscopy of late-type stars in the young open cluster Blanco 1 using XMM-Newton.
• To improve detection completeness of cluster members compared to previous ROSAT observations.
• To analyze X-ray luminosity distributions (XLDs) for dF, dG, dK, and dM stars in the cluster.
• To investigate the spectral properties of unidentified X-ray sources and assess their potential cluster membership.
• To explore the impact of high metallicity ([Fe/H] = +0.23 dex) on X-ray activity and coronal emission in young stars.

Proposed method

• Utilized XMM-Newton's EPIC camera (MOS1, MOS2, and pn) to collect X-ray data over a 50 ksec observation.
• Applied a wavelet-based source detection algorithm to combined MOS and pn datasets to maximize sensitivity and detection completeness.
• Performed low-resolution X-ray spectroscopy on 6 bright cluster sources using XSPEC fitting tools to model plasma emission.
• Fitted X-ray spectra with single- and two-temperature thermal plasma models (APEC) to characterize coronal temperatures and emission measures.
• Used X-ray color-color diagrams with two color indices to classify spectral types and compare with known cluster members.
• Cross-identified X-ray sources with optical/infrared catalogs (GSC-II, USNO-B1, 2MASS) to assess membership and spectral type.

Experimental results

Research questions

• RQ1 What is the X-ray spectral energy distribution of active stars in the high-metallicity open cluster Blanco 1?
• RQ2 How does the X-ray luminosity distribution of dM stars in Blanco 1 compare to that of the Pleiades and other young clusters?
• RQ3 What is the nature of the unidentified X-ray sources in the field, and do any show spectral characteristics consistent with cluster coronae?
• RQ4 To what extent does the high metallicity of Blanco 1 influence the observed X-ray coronal emission properties?
• RQ5 Can the X-ray emission in the cluster be explained by a two-temperature plasma model, and how does this compare to other young stellar clusters?

Key findings

• XMM-Newton detected 190 X-ray sources, with 88% completeness for cluster members—up from 61% in prior ROSAT observations.
• The X-ray spectra of the brightest cluster stars are best fit by a two-temperature plasma model with temperatures of ~0.3 keV and ~1 keV, indicating quiescent coronal activity.
• The emission measures for both temperature components are similar, suggesting a balanced contribution from cool and hot plasma in the corona.
• A flaring low-mass star (nr. 26) showed a soft X-ray spectrum best fit by a 1-T model at ~0.65 keV with high absorption (NH ~1.6×10²¹ cm⁻²), but its low abundance (0.03 Z☉) suggests possible non-solar composition.
• One star (BLX 16, nr. 169) with a M1Ve spectral type and X-ray luminosity log LX = 29.13 is consistent with cluster membership and dM-type X-ray emission, suggesting it may be a new low-mass cluster member.
• Unidentified sources (64 in total) show diverse X-ray colors; two have spectral properties consistent with cluster coronae, indicating possible new cluster members or active field stars.