The ISO-LWS far-infrared spectra of pre-Main Sequence objects

Astronomy & Astrophysics, 2013

Context. The temperature and density structure of molecular cloud cores are the most important physical quantities that determine the course of the protostellar collapse and the properties of the stars they form. Nevertheless, density profiles often rely either on the simplifying assumption of isothermality or on observationally poorly constrained model temperature profiles. The instruments of the Herschel satellite provide us for the first time with both the spectral coverage and the spatial resolution that is needed to directly measure the dust temperature structure of nearby molecular cloud cores. Aims. With the aim of better constraining the initial physical conditions in molecular cloud cores at the onset of protostellar collapse, in particular of measuring their temperature structure, we initiated the Guaranteed Time Key Project (GTKP) "The Earliest Phases of Star Formation" (EPoS) with the Herschel satellite. This paper gives an overview of the low-mass sources in the EPoS project, the Herschel and complementary ground-based observations, our analysis method, and the initial results of the survey. Methods. We study the thermal dust emission of 12 previously well-characterized, isolated, nearby globules using FIR and submm continuum maps at up to eight wavelengths between 100 µm and 1.2 mm. Our sample contains both globules with starless cores and embedded protostars at different early evolutionary stages. The dust emission maps are used to extract spatially resolved SEDs, which are then fit independently with modified blackbody curves to obtain line-of-sight-averaged dust temperature and column density maps. Results. We find that the thermal structure of all globules (mean mass 7 M ) is dominated by external heating from the interstellar radiation field and moderate shielding by thin extended halos. All globules have warm outer envelopes (14-20 K) and colder dense interiors (8-12 K) with column densities of a few 10 22 cm −2 . The protostars embedded in some of the globules raise the local temperature of the dense cores only within radii out to about 5000 AU, but do not significantly affect the overall thermal balance of the globules. Five out of the six starless cores in the sample are gravitationally bound and approximately thermally stabilized. The starless core in CB 244 is found to be supercritical and is speculated to be on the verge of collapse. For the first time, we can now also include externally heated starless cores in the L smm / L bol vs. T bol diagram and find that T bol < 25 K seems to be a robust criterion to distinguish starless from protostellar cores, including those that only have an embedded very low-luminosity object.

The Astrophysical Journal, 2005

This is a report on detailed modeling of young high-mass protostellar candidates during their most embedded and obscured phases. We performed narrowband mid-infrared imaging of three candidate high-mass protostellar objects in G11.94-0.62, G29.96-0.02, and G45.07+0.13 at Gemini Observatory using the Thermal-Region Camera and Spectrograph (T-ReCS). The sources were imaged through up to 11 narrowband filters, sampling their SEDs over the entire 2-25 µm infrared range. For the first time, we have fit the observed SEDs of massive protostars with models that take into account departures from spherical symmetry in the infalling envelopes. In this way, we have been able to back out of the models detailed physical parameters for these earliest stages of massive stellar life. Our detailed modeling suggests that massive star formation can proceed in a way very similar to the formation of low-mass stars.

Astrophysical Journal, 2011

In this paper we present Spitzer Infrared Spectrograph spectroscopy for 14 intermediate-mass young stellar objects. We use Spitzer spectroscopy to investigate the physical properties of these sources and their environments. Our sample can be divided into two types of objects: young isolated, embedded objects with spectra that are dominated by ice and silicate absorption bands, and more evolved objects that are dominated by extended emission from polycyclic aromatic hydrocarbons (PAHs) and pure H2 rotational lines. We are able to constrain the illuminating FUV fields by classifying the PAH bands below 9micron. For most of the sources we are able to detect several atomic fine structure lines. In particular, the [NeII] line appearing in two regions could originate from unresolved photodissociation regions (PDRs) or J-shocks. We relate the identified spectral features to observations obtained from NIR through submillimeter imaging. The spatial extent of several H2 and PAH bands is matched with morphologies identified in previous Spitzer/IRAC observations. This also allows us to distinguish between the different H2 excitation mechanisms. In addition, we calculate the optical extinction from the silicate bands and use this to constrain the spectral energy distribution fit, allowing us to estimate the masses of these YSOs.

Astronomy and Astrophysics, 2009

Aims. The earliest stages of intermediate-and high-mass star formation remain poorly understood. To gain deeper insights, we study a previously discovered protostellar source that is deeply embedded and drives an energetic molecular outflow. Methods. The source, UYSO 1, located close to IRAS 07029-1215 at a distance of about 1 kpc, was observed in the (sub)millimeter and centimeter wavelength ranges, as well as at near-, mid-, and far-infrared wavelengths.

Astronomy and Astrophysics, 2002

We present an atlas of spectra of O-and Btype stars, obtained with the Short Wavelength Spectrometer (SWS) during the Post-Helium program of the Infrared Space Observatory (ISO). This program is aimed at extending the Morgan & Keenan classification scheme into the near-infrared. Later type stars will be discussed in a seperate publication. The observations consist of 57 SWS Post-Helium spectra from 2.4 to 4.1 µm, supplemented with 10 spectra acquired during the nominal mission with a similar observational setting. For B-type stars, this sample provides ample spectral converage in terms of subtype and luminosity class. For O-type stars, the ISO sample is coarse and therefore is complemented with 8 UKIRT L'band observations. In terms of the presence of diagnostic lines, the L'-band is likely the most promising of the nearinfrared atmospheric windows for the study of the physical properties of B stars. Specifically, this wavelength interval contains the Brα, Pfγ, and other Pfund lines which are probes of spectral type, luminosity class and mass loss. Here, we present simple empirical methods based on the lines present in the 2.4 to 4.1 µm interval that allow the determination of i) the spectral type of B dwarfs and giants to within two subtypes; ii) the luminosity class of B stars to within two classes; iii) the mass-loss rate of O stars and B supergiants to within 0.25 dex.

2011

Characterising stellar and circumstellar properties of embedded young stellar objects (YSOs) is mandatory for understanding the early stages of the stellar evolution. This task requires the combination of both spectroscopy and photometry, covering the widest possible wavelength range, to disentangle the various protostellar components and activities. As part of the POISSON project, we present a multi-wavelength spectroscopic and photometric investigation

The Astrophysical Journal Supplement Series, 2008

We present echelle long-slit optical spectra of a sample of objects evolving off the Asymptotic Giant Branch (AGB), most of them in the pre-planetary nebula (pPN) phase, obtained with the ESI and MIKE spectrographs at the 10 m Keck II and 6.5 m Magellan-I telescopes, respectively. The total wavelength range covered with ESI (MIKE) is ∼3900 to 10900Å (∼3600 to 7200Å). In this paper, we focus our analysis mainly on the Hα profiles. Prominent Hα emission is detected in half of the objects, most of which show broad Hα wings (with total widths of up to ∼4000 km s −1 ). In the majority of the Hα-emission sources, fast, post-AGB winds are revealed by P-Cygni profiles. In ∼37% of the objects Hα is observed in absorption. In almost all cases, the absorption profile is partially filled with emission, leading to complex, structured profiles that are interpreted as an indication of incipient post-AGB mass-loss. The rest of the objects (∼13%) are Hα non-detections. We investigate correlations between the Hα profile and different stellar and envelope parameters. All sources in which Hα is seen mainly in absorption have F-G type central stars, whereas sources with intense Hα emission span a larger range of spectral types from O to G, with a relative maximum around B, and also including very late C types. Shocks may be an important excitation/ionization agent of the close stellar surroundings for objects with late type central stars. Sources with pure emission or P Cygni Hα profiles have larger J − K color excess than objects with Hα mainly in absorption, which suggests -2the presence of warm dust near the star in the former. The two classes of profile sources also segregate in the IRAS color-color diagram in a way that intense Hα-emitters have dust grains with a larger range of temperatures. Spectral classification of the central stars in our sample is presented. For a subsample (13 objects), the stellar luminosity has been derived from the analysis of the O I 7771-5Å infrared triplet. The location in the HR diagram of most of these targets, which represent ∼30% of the whole sample, is consistent with relatively high final (and, presumably, initial) masses in the range M f ∼0.6-0.9M ⊙ (M i ∼3-8M ⊙ ).

2008

The Astrophysical Journal, 2010

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 spectral energy distribution 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 (IRS) on board 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 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 μm 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.

2008

This is a report on detailed modeling of young high-mass protostellar candidates during their most embedded and obscured phases. We performed narrowband mid-infrared imaging of three candidate high-mass protostellar objects in G11.94-0.62, G29.96-0.02, and G45.07+0.13 at Gemini Observatory using the Thermal-Region Camera and Spectrograph (T-ReCS). The sources were imaged through up to 11 narrowband filters, sampling their SEDs over the entire 2–25 µm infrared range. For the first time, we have fit the observed SEDs of massive protostars with models that take into account departures from spherical symmetry in the infalling envelopes. In this way, we have been able to back out of the models detailed physical parameters for these earliest stages of massive stellar life. Our detailed modeling suggests that massive star formation can proceed in a way very similar to the formation of low-mass stars.