Properties of Protostars in the Elephant Trunk in the Globule IC 1396A

Extremely red objects, identified in the early Spitzer Space Telescope observations of the bright-rimmed globule IC 1396A and photometrically classified as Class I protostars and Class II T Tauri stars based on their mid-infrared (mid-IR) colors, were spectroscopically observed at 5.5-38 μm (Spitzer Infrared Spectrograph), at the 22 GHz water maser frequency (National Radio Astronomy Observatory Green Bank Telescope), and in the optical (Palomar Hale 5 m) to confirm their nature and further elucidate their properties. The sources photometrically identified as Class I, including IC 1396A:α, γ, δ, ε, and ζ, are confirmed as objects dominated by accretion luminosity from dense envelopes, with accretion rates 1-10 × 10^–6 M☉ yr^–1 and present stellar masses 0.1-2 M☉. The Class I sources have extremely red continua, still rising at 38 μm, with a deep silicate absorption at 9-11 μm, weaker silicate absorption around 18 μm, and weak ice features including CO2 at 15.2 μm and H2O at 6 μm. The ice/silicate absorption ratio in the envelope is exceptionally low for the IC 1396A protostars, compared to those in nearby star-forming regions, suggesting that the envelope chemistry is altered by the radiation field or globule pressure. Only one 22 GHz water maser was detected in IC 1396A; it is coincident with a faint mid-IR source, offset from near the luminous Class I protostar IC 1396A:γ. The maser source, IC 1396A:γb, has luminosity less than 0.1 L☉, the first H2O maser from such a low-luminosity object. Two near-infrared (NIR) H2 knots on opposite sides of IC 1396A:γ reveal a jet, with an axis clearly distinct from the H2O maser of IC 1396A:γb. The objects photometrically classified as Class II, including IC 1396A:β, θ, Two Micron All Sky Survey (2MASS)J 21364964+5722270, 2MASSJ 21362507+5727502, LkHα 349c, Tr 37 11-2146, and Tr 37 11-2037, are confirmed as stars with warm, luminous disks, with a silicate emission feature at 9-11 μm, and bright Hα emission; therefore, they are young, disk-bearing, classical T Tauri stars. The disk properties change significantly with source luminosity: low-mass (G-K) stars have prominent 9-11 emission features due to amorphous silicates while higher-mass (A-F) stars have weaker features requiring abundant crystalline silicates. A mineralogical model that fits the wide- and low-amplitude silicate feature of IC 1396A:θ requires small grains of crystalline olivine (11.3 μm peak) and another material to to explain its 9.1 μm peak; reasonable fits are obtained with a phyllosilicate, quartz, or relatively large (greater than 10 μm) amorphous olivine grains. The distribution of Class I sources is concentrated within the molecular globule, while the Class II sources are more widely scattered. Combined with the spectral results, this suggests two phases of star formation, the first (4 Myr ago) leading to the widespread Class II sources and the central O star of IC 1396 and the second (less than 1 Myr ago) occurring within the globule. The recent phase was likely triggered by the wind and radiation of the central O star of the IC 1396 H II region

Disentangling protostellar evolutionary stages in clustered environments using Spitzer-IRS spectra and comprehensive SED modeling

When studying the evolutionary stages of protostars that form in clusters, the role of any intracluster medium cannot be neglected. High foreground extinction can lead to situations where young stellar objects (YSOs) appear to be in earlier evolutionary stages than they actually are, particularly when using simple criteria like spectral indices. To address this issue, we have assembled detailed SED characterizations of a sample of 56 Spitzer-identified candidate YSOs in the clusters NGC 2264 and IC 348. For these, we use spectra obtained with the Infrared Spectrograph onboard the Spitzer Space Telescope and ancillary multi-wavelength photometry. The primary aim is twofold: 1) to discuss the role of spectral features, particularly those due to ices and silicates, in determining a YSO's evolutionary stage, and 2) to perform comprehensive modeling of spectral energy distributions (SEDs) enhanced by the IRS data. The SEDs consist of ancillary optical-to-submillimeter multi-wavelength data as well as an accurate description of the 9.7 micron silicate feature and of the mid-infrared continuum derived from line-free parts of the IRS spectra. We find that using this approach, we can distinguish genuine protostars in the cluster from T Tauri stars masquerading as protostars due to external foreground extinction. Our results underline the importance of photometric data in the far-infrared/submillimeter wavelength range, at sufficiently high angular resolution to more accurately classify cluster members. Such observations are becoming possible now with the advent of the Herschel Space Observatory.Comment: Accepted for publication in Ap

A Spitzer Space Telescope Infrared Survey of Supernova Remnants in the Inner Galaxy

Using Infrared Array Camera (IRAC) images at 3.6, 4.5, 5.8, and 8 microns from the GLIMPSE Legacy science program on the Spitzer Space Telescope, we searched for infrared counterparts to the 95 known supernova remnants that are located within galactic longitudes 65>|l|>10 degrees and latitudes |b|<1 degree. Eighteen infrared counterparts were detected. Many other supernova remnants could have significant infrared emission but are in portions of the Milky Way too confused to allow separation from bright HII regions and pervasive mid-infrared emission from atomic and molecular clouds along the line of sight. Infrared emission from supernova remnants originates from synchrotron emission, shock-heated dust, atomic fine-structure lines, and molecular lines. The detected remnants are G11.2-0.3, Kes 69, G22.7-0.2, 3C 391, W 44, 3C 396, 3C 397, W 49B, G54.4-0.3, Kes 17, Kes 20A, RCW 103, G344.7-0.1, G346.6-0.2, CTB 37A, G348.5-0.0, and G349.7+0.2. The infrared colors suggest emission from molecular lines (9 remnants), fine-structure lines (3), and PAH (4), or a combination; some remnants feature multiple colors in different regions. None of the remnants are dominated by synchrotron radiation at mid-infrared wavelengths. The IRAC-detected sample emphasizes remnants interacting with relatively dense gas, for which most of the shock cooling occurs through molecular or ionic lines in the mid-infrared.Comment: Accepted 10/18/2005 for publication in "The Astronomical Journal". The figures in this astro-ph submission are drastically reduced in quality in order to fit within its limit

Interstellar absorption across the electromagnetic spectrum

We report results of a multi-wavelength study of interstellar absorption in diffuse molecular clouds that lie in the direction of flat-spectrum quasars. Quasars as back-ground sources allow the measurement of Galactic interstellar absorption across the electromagnetic spectrum from mm to X-ray wavelengths. We have obtained high-resolution (≈3 km s-1) near-UV to far-red spectra (3300-10400 \uc5) of nine quasars as well as several Galactic sources with the UV-Visual Echelle Spectrograph (UVES) at the Very Large Telescope (VLT) UT2 of the European Southern Observatory (ESO). This is the first optical study of the classical molecules CH and CH+ along the same lines of sight used for mm absorption studies of polyatomic molecules like HCO+, C2H, and H2CO, which have been observed by H.S. Liszt and R. Lucas at unexpectedly high abundances in diffuse molecular gas. For the quasars PKS 0736+017 and PKS 2251+158 we see CH absorption at the same velocities as HCO+ observed at mm wavelengths. The CH and CH+ lines are also connected to distinct Galactic absorption components of Ca II, Na I, and K I that we see in our spectra. We also used the data obtained for this project to study redshifted emission and absorption lines originating in the AGN and from intervening absorption systems. We present a detailed study of the zabs=0.79 metal-rich intervening absorber toward PKS 2145+067. One of the Galactic background sources of our project is the pulsar of the Crab Nebula supernova remnant. We show the the first spectra of high spatial (sub-arcsecond) and spectral (≈3 km s-1) resolution of the material within 10\u27 of the Crab pulsar. We detect a host of nebular emission lines, including [O II], [O III], [S II], [S III], H β/γ, He I, He II, [C I], [Ne III], [Ar III], and [Ni II], at kinematic heliocentric velocities ranging from about +1500 to -1200 km s-1

Interstellar absorption across the electromagnetic spectrum

We report results of a multi-wavelength study of interstellar absorption in diffuse molecular clouds that lie in the direction of flat-spectrum quasars. Quasars as back-ground sources allow the measurement of Galactic interstellar absorption across the electromagnetic spectrum from mm to X-ray wavelengths. We have obtained high-resolution (≈3 km s-1) near-UV to far-red spectra (3300-10400 \uc5) of nine quasars as well as several Galactic sources with the UV-Visual Echelle Spectrograph (UVES) at the Very Large Telescope (VLT) UT2 of the European Southern Observatory (ESO). This is the first optical study of the classical molecules CH and CH+ along the same lines of sight used for mm absorption studies of polyatomic molecules like HCO+, C2H, and H2CO, which have been observed by H.S. Liszt and R. Lucas at unexpectedly high abundances in diffuse molecular gas. For the quasars PKS 0736+017 and PKS 2251+158 we see CH absorption at the same velocities as HCO+ observed at mm wavelengths. The CH and CH+ lines are also connected to distinct Galactic absorption components of Ca II, Na I, and K I that we see in our spectra. We also used the data obtained for this project to study redshifted emission and absorption lines originating in the AGN and from intervening absorption systems. We present a detailed study of the zabs=0.79 metal-rich intervening absorber toward PKS 2145+067. One of the Galactic background sources of our project is the pulsar of the Crab Nebula supernova remnant. We show the the first spectra of high spatial (sub-arcsecond) and spectral (≈3 km s-1) resolution of the material within 10\u27 of the Crab pulsar. We detect a host of nebular emission lines, including [O II], [O III], [S II], [S III], H β/γ, He I, He II, [C I], [Ne III], [Ar III], and [Ni II], at kinematic heliocentric velocities ranging from about +1500 to -1200 km s-1