Matthew S. Povich1, Jessica T. Maldonado1,2,3, Evan H. Nuñez1,4, and Thomas P
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The Duration of Star Formation in Galactic Giant Molecular Clouds from X-ray and Infrared Observations Matthew S. Povich1, Jessica T. Maldonado1,2,3, Evan H. Nuñez1,4, and Thomas P. Robitaille5 1Cal Poly Pomona, USA; 2Michigan State, USA; 3Cal-Bridge Alumna; 4Cal-Bridge Scholar; 5Headingley Enterprise and Arts Centre, UK MOTIVATION Intermediate-Mass PMS Stars (IMPS) The challenge of empirically determining ages of pre- • IMPS (2 M¤ < m < 8 M¤) evolve rapidly across the HRD main-sequence (PMS) stellar populations remains a 2269 CCCP stars w/o mid-IR on horizontal tracks. Mid-IR photometry constrains primary obstacle to comparing observations with excess, color-coded by sub- luminosity/mass, and near-IR colors change measurably theories of star formation and accurately measuring star region clustering Trumpler 15 on Myr timescales (see Figs. 4 below). formation rates. This problem is most acute for young, -0.2 Contours: density of X-ray • Coronal X-ray emission (Gregory et al. 2016) and mid-IR members (Feigelson et al. 2011) massive star-forming regions located at d > 1 kpc behind Tr 15 + excess emission from disks (Hillenbrand et al. 1992, very high interstellar extinction. +1432 YSOs w/ disks Environs (Povich et al. 2011) Povich et al. 2016) both decay more rapidly for IMPS CCCP Pilot Study Galactic latitude Collinder 232 than lower-mass, T Tauri stars. The Chandra Carina Complex Project (Townsley et al. -0.4 2011) revealed >12,000 stellar members in the Carina η Car (saturated), Trumpler 16 Limitations of pHRD Method Nebula Complex via combined X-ray and infrared (IR) • Unreliable for low-mass stars/regions. photometric catalogs. Gaia DR2 parallaxes place this • X-ray selection creates a biased sample. Mass population at d = 2.5 ± 0.3 kpc. Treasure Chest distributions depend on age and X-ray source Probabilistic H-R Diagrams (pHRDs) -0.6 Trumpler 14 sensitivity! We aggregate evolutionary models of young stellar Tr 14 + Environs populations, incorporating age diagnostics used in highly- Bochum 11 obscured regions: I. Circumstellar disk dissipation timescales -0.8 II. Presence of strong coronal X-ray emission Modeling the Duration of Star Formation (tSF) • IR (1.2–8.0 µm) spectral energy distributions (SEDs) of X-ray-selected young stars with no mid-IR excess emission from disks are fit with reddened stellar -1.0 photospheres tied to PMS evolutionary models. • The set of well-fit models to each star is used to Tr 16 construct a normalized, 2D probability distribution 4a (2DPD) for its location on the H–R diagram. Collinder 228 • The 2DPD is age-weighted using likelihood functions -1.2 derived from diagnostics I. and II. above. • Summing the weighted 2DPDs of all stars in a population generates its composite pHRD and associated mass and age distributions. -1.4 Gaia–ESO Spectroscopic Comparison Sample South 1 Galactic longitude Pillars • We identified 89 GK-type stellar members in Tr 16 and 288.4 288.2 288.0 287.8 287.6 287.4 287.2 287.0 14 (inside white box in Fig. 1) with Teff measured from VLT spectroscopy (Damiani et al. 2017) to compare 1.6 with our SED modeling results (Fig. 2, below). KEY: Each panel shows sources from a single large-scale stellar • An additional 14 B-type members were all correctly density region in the CCCP (Feigelson et al. 2011). modeled as hot stars and included in our mass and age Mass Distribution 4B distributions (Figs. 3, right). X-ray selected, diskless pHRD stars with scaled Salpeter Mass Mass Siess et al. (2000) PMS IMF overplotted CutoFF = CutoFF = tracks (dashed curves) Luminosity and isochrones (solid Age Distribution Distributed IR-only SED ft parameters curves) overlaid X-ray selected, diskless Population Time-evolution of our “naked” stellar 89 cool stars stars above the mass photosphere spectral models over the first 10 cutoff * Spectroscopic T distribution ef Temperature Myr for 2 M¤ (Fig 4A) and 3 M¤ (Fig 4B) stars. Unweighted SED fit parameters DistriBution of all models = tSF = tSF Results • Clear differences in tSF among the sub-regions studied. Star formation history of Carina Nebula References HillenBrand et al. 1992, 397, 613 Damiani et al. 2017, A&A, 603, A81 began ~10 Myr ago, with the biggest fireworks occurring within the past 3 Myr when the massive Hur et al. 2012, AJ, 143, 41 Feigelson et al. 2011, ApJS, 194, 9 Povich et al. 2011, ApJS, 194, 14 Tr 16 and Tr 14 clusters formed. Getman et al. 2014, ApJ, 787, 108 Povich et al. 2016, ApJ, 825, 125 Gregory et al. 2016, MNRAS, 457, • t agrees with independent estimates of stellar ages, e.g. AgeJX subcluster median ages (Getman Siess et al. 2000, A&A, 358, 593 SF 3836 et al. 2014) and BVI color-mag diagrams of Tr 16/14 (Hur et al. 2012, Damiani et al. 2017). Townsley et al. 2011, ApJS, 194, 1 3a 3b • Evidence of 5–10 Myr old populations associated with regions of ongoing star formation. Download a copy of this poster → Mass (top) and age Same as in Fig. 3A, but with Future Work This work was supported by the NSF via distributions for 103 T constrained by 2 eff • pHRD analysis of ~20 other Galactic clouds for star-formation rate calibrations. awards CAREER-1454224 and DUE-1356133 comparison stars, usual age- spectroscopic measurements. (Cal-Bridge). weighting. tSF determination is stable. • Mass distributions including disk-bearing YSOs (harder problem, many parameters in SED models)..