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26 New Young Stellar Population in Serpens the Serpens region with Spitzer. These spectra will also be used to estimate mass accretion rates using the strength of the Hα emission line (Muzerolle et al. 2003; White & Basri 2003, Natta et al. 2004), and the extinction toward each object. The paper is constructed as follows: Section 2.2 describes the selection criteria for our sample, and in Section 2.3 we describe the observations and data reduction. In Section 2.4 we discuss our spectral classification methods, along with its results for this sample and derive effective temperatures. In Section 2.5, we present our extinction studies based on the Spitzer photometry and on our optical spectra. In Section 2.6 we derive luminosities for the objects. This allows us to place each object in a Hertzsprung-Russell (HR) diagram, and derive its age and mass from comparison with evolutionary models. The Hα line and accretion rates are discussed in Section 2.7. Finally, in Section 2.8 we present our conclusions. 2.2 Sample Selection From the c2d catalog, Harvey et al. (2007b) plotted spectral energy distributions (SEDs; assuming a K7 spectral type for all the sources) and identified 235 YSO candidates – objects with IR excess, interpreted as due to disks or envelopes. These authors discuss the problem that background galaxies and bright background post- AGB stars may show the same color distribution as that of YSOs. Particularly, the post-AGB stars could contaminate the bright end of the luminosity distribution. To this original sample of 235 objects, a flux threshold of 3mJy at 8µm was applied, resulting in 150 sources bright enough to be observed in follow-up observations with the InfraRed Spectrograph (IRS), onboard Spitzer. The IRS observations, carried out to study the evolution of dust in protoplanetary disks of a complete, flux-limited sample will be presented in a future paper (Oliveira et al. 2009). Here, we present optical spectroscopy of 78 stars bright enough to obtain optical spectroscopy with a 4 m class telescope. The remaining objects are too extinct in the optical to be detected, and are being classified in an ongoing near-IR (NIR) spectroscopic survey. The resulting sample contains objects that span a range in evolutionary stages from embedded Class I (i.e., spectral slope α 2−24µm > 0.3) sources to young stars with protoplanetary disks (Class II sources, -1.6 < α 2−24µm < 0.3) and stars with photospheric fluxes in the Infrared Array Camera (IRAC) bands and excess in the MIPS bands (also called “cold disks”, e.g., Brown et al. 2007). Figure 2.1 shows the spatial distribution of the complete sample of 150 Serpens YSOs observed with Spitzer/IRS. The filled and open symbols correspond to detected and undetected objects from the optical survey presented in this paper, respectively. 2.3 Observations and Data Reduction The spectroscopic data were obtained during observing runs at three telescopes: two runs with the multi-object Wide Field Fiber Optical Spectrograph (WYFFOS) at
Evolution of Dust in Protoplanetary Disks 27 Figure 2.1 – Observed objects shown on the 8.0µm IRAC map of the Serpens Molecular Cloud, imaged as part of the Spitzer Legacy Program “From Molecular Clouds to Planet-Forming Disks” (c2d) (Harvey et al. 2006). Filled symbols are the 78 objects for which we present optical spectroscopy in this paper: filled circles are confirmed members of the cloud and filled triangles are likely candidate background contaminants (§ 2.6). The open symbols are the remaining young stellar object candidates in the sample, not detected in our survey of 150 YSOs. Overlaid are the contours (5, 10, 15, 20 and 25 mag) of visual extinction derived from the “c2d” extinction maps.
Page 1: Observational <str
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Page 8 and 9: viii Chapter 3. YSOs in the Lupus M
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4 A Spitzer Survey of Protoplanetar
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Evolution of Dust in Protoplanetary
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