Laboratory investigations aimed at building a database for the interpretation of JWST spectra

2019 ◽  
Vol 15 (S350) ◽  
pp. 77-80
Author(s):  
Maria Elisabetta Palumbo ◽  
Giuseppe A. Baratta ◽  
Gleb Fedoseev ◽  
Daniele Fulvio ◽  
Carlotta Scirè ◽  
...  
Keyword(s):  
Thermal Processing ◽  
Laboratory Data ◽  
Cosmic Ray ◽  
Peak Position ◽  
Young Stellar Objects ◽  
Line Of Sight ◽  
High Quality ◽  
Stellar Objects ◽  
James Webb Space Telescope ◽  
Laboratory Investigations

AbstractThe James Webb Space Telescope (JWST) is expected to be launched in 2021. The JWST’s science instruments will provide high quality spectra acquired in the line of sight to young stellar objects whose interpretation will require a robust database of laboratory data. With this in mind, an experimental work is in progress in the Laboratory for Experimental Astrophysics in Catania to study the profile (shape, width, and peak position) of the main infrared bands of molecular species expected to be present in icy grain mantles. Our study also takes into account the modifications induced on icy samples by low-energy cosmic ray bombardment and by thermal processing. Here we present some recent results on deuterium hydrogen monoxide (HDO), N-bearing species, and carbon dioxide (CO2).

scholarly journals Recent results on polarization of T Tauri stars and other young stellar objects

1990 ◽  
Vol 137 ◽  
pp. 179-184
Author(s):  
Pierre Bastien ◽  
François Ménard
Keyword(s):  
Rotation Period ◽  
T Tauri Stars ◽  
Young Stars ◽  
Young Stellar Objects ◽  
Current Evidence ◽  
Line Of Sight ◽  
Stellar Objects ◽  
T Tauri ◽  
Thick Part ◽  
The Difference

Recent results on observations and models of polarization of T Tauri stars (TTS) and other young stellar objects (YSO's) are presented. In particular, the difference in polarization properties between the classical T Tauri stars (CTTS) and the weak-line T Tauri stars (WTTS) is made. A correlation between polarization and rotation period is searched for but not found. Observations of polarization maps for many young stars are considered. Two types of models have been proposed to explain these observations. Current evidence favors single and multiple scattering in flattened, optically thick, structures, i.e. disks, around many TTS. In particular, the size of the optically thick part of the disks, and their inclination to our line of sight can determined for published polarization maps.

Evidence for the absorption of crystalline silicates at 11.1 $\mu$m in the spectra of the nucleus of the Circinus galaxy

2019 ◽  
Vol 488 (1) ◽  
pp. L75-L79
Author(s):  
Tho Do Duy ◽  
Warrick A Lawson
Keyword(s):  
Grain Size ◽  
Milky Way ◽  
Young Stellar Objects ◽  
Line Of Sight ◽  
Stellar Objects ◽  
Mid Infrared ◽  
Profile Shape ◽  
The Earth ◽  
Star Formation Regions ◽  
Galaxy Nucleus

Abstract Several mid-infrared spectra of the Circinus galaxy nucleus taken with T-ReCS on Gemini South and MIDI on VLTI have consistently shown an inflection centred around 11 $\mu$m. We ascribe this feature to the absorption of crystalline silicate, based on their similarity in profile shape and improvement in fitting quality using a partially crystalline silicate model, compared to entirely amorphous models. Spectral fits reveal a fraction of 0.6–2.0 per cent of crystalline forsterite in the nucleus of the Circinus galaxy, which is similar to the values obtained for the interstellar medium (ISM) of the Milky Way. This is probably the first detection of crystalline silicate absorption in the nucleus of this Seyfert 2 galaxy. In addition, the presence of large grain-size amorphous silicates, together with the similarity in profile shape of the optical depth of Circinus with those of young stellar objects in the Milky Way, implies that most of the contribution to the spectra of Circinus comes from dust in the star formation regions near the centre of the nucleus or along the line of sight to the Earth, rather than in the ISM of Circinus. We also compare our optical depths of Circinus with those in previous studies.

THE EVOLUTION OF MASSIVE YOUNG STELLAR OBJECTS IN THE LARGE MAGELLANIC CLOUD. II. THERMAL PROCESSING OF CIRCUMSTELLAR ICES

2010 ◽  
Vol 727 (1) ◽  
pp. 36 ◽  
Author(s):  
Jonathan P. Seale ◽  
Leslie W. Looney ◽  
C.-H. Rosie Chen ◽  
You-Hua Chu ◽  
Robert A. Gruendl
Keyword(s):  
Thermal Processing ◽  
Large Magellanic Cloud ◽  
Magellanic Cloud ◽  
Young Stellar Objects ◽  
Stellar Objects

scholarly journals The Fractional Ionization in Molecular Cloud Cores

2000 ◽  
Vol 197 ◽  
pp. 41-50 ◽  
Author(s):  
Paola Caselli
Keyword(s):  
Dynamical Evolution ◽  
Cosmic Ray ◽  
Ionization Rate ◽  
Young Stellar Objects ◽  
Ionization Degree ◽  
Degree Of Ionization ◽  
Stellar Objects ◽  
Interstellar Clouds ◽  
Ion Molecule Reactions ◽  
Cloud Cores

Ions and electrons play a key role in the chemical and dynamical evolution of interstellar clouds. Gas phase ion–molecule reactions are major chemical routes to the formation of interstellar molecules. The ionization degree determines the coupling between the magnetic field and the molecular gas through ion–neutral collisions, and thus regulates the rate of star formation. In the theoretical determination of the degree of ionization we run into several sources of uncertainty, including the poorly known cosmic ray flux and metal depletion within the cores, the penetration of UV radiation deep into regions of high visual extinction due to cloud inhomogeneities, and the ionization rate increase in the proximity of young stellar objects which may be strong X–ray emitters. Observational estimates of electron (or ion) fractions x(e) (≡ n(e)/n(H2), where n(e) and n(H2) are the electron and molecular hydrogen number densities, respectively) in dense cloud cores are thus of considerable interest. In this paper, I will review recent improvements in the estimates of the ion fraction in dense cores and point out the difficulties in determining x(e).

scholarly journals Crystalline silicate absorption at 11.1 μm: ubiquitous and abundant in embedded YSOs and the interstellar medium

2020 ◽  
Vol 493 (3) ◽  
pp. 4463-4517 ◽  
Author(s):  
Tho Do-Duy ◽  
Christopher M Wright ◽  
Takuya Fujiyoshi ◽  
Alistair Glasse ◽  
Ralf Siebenmorgen ◽  
...  
Keyword(s):  
Star Formation ◽  
Interstellar Medium ◽  
Mass Fraction ◽  
Cosmic Ray ◽  
Young Stellar Objects ◽  
Absorption Feature ◽  
H Ii Regions ◽  
Stellar Objects ◽  
Stellar Outflows ◽  
T Tauri

ABSTRACT Utilizing several instruments on 4–8 m telescopes, we have observed a large sample of objects in the mid-infrared (8–13 μm). These comprise a few evolved stars, multiple envelopes of embedded young stellar objects (YSOs) or compact H-II regions, and several sightlines through the interstellar medium (ISM). The latter is where dust resides – and is potentially modified – between its formation in evolved stellar outflows and deposition in molecular clouds. In most objects, we detect not only the well-known 9.7 μm absorption feature of amorphous silicates but also a second absorption band around 11.1 μm whose carrier is attributed to crystalline forsterite. We propose that crystalline silicates are essentially ubiquitous in the ISM and earliest phases of star formation, and are evolutionary precursors to T-Tauri and Herbig stars where such silicates have been commonly found. Modelling shows that in most YSOs, H-II regions and ISM cases, the forsterite mass fraction is between 1 and 2 per cent, suggesting that the younger phases inherit their abundance from the ISM. However, several sources show much stronger features (abundances ≥3 per cent). This suggests that significant processing, perhaps crystallization by thermal annealing, occurs early on in star formation. Most intriguing is the first detection of crystalline silicate in the diffuse ISM. We propose that our observed abundance is consistent with a mass fraction of crystalline silicates of 10–20 per cent injected into the ISM, along with commonly accepted lifetimes against their destruction, but only if cosmic ray-induced amorphization is insignificant over a few Giga years.

scholarly journals Investigating episodic accretion in a very low-mass young stellar object

2020 ◽  
Vol 643 ◽  
pp. A181
Author(s):  
C. Stock ◽  
A. Caratti o Garatti ◽  
P. McGinnis ◽  
R. Garcia Lopez ◽  
S. Antoniucci ◽  
...  
Keyword(s):  
Near Infrared ◽  
Accretion Rate ◽  
Photometric Data ◽  
Class I ◽  
Young Stellar Objects ◽  
Line Of Sight ◽  
Stellar Objects ◽  
Steep Decrease ◽  
Order Of Magnitude ◽  
Low Mass

Context. Very low-mass Class I protostars have been investigated very little thus far. Variability of these young stellar objects (YSOs) and whether or not they are capable of strong episodic accretion is also left relatively unstudied. Aims. We investigate accretion variability in IRS 54 (YLW52), a Class I very low-mass protostar with a mass of M⋆ ∼ 0.1 − 0.2 M⊙. Methods. We obtained spectroscopic and photometric data with VLT/ISAAC and VLT/SINFONI in the near-infrared (J, H, and K bands) across four epochs (2005, 2010, 2013, and 2014). We used accretion-tracing lines (Paβ and Brγ) and outflow-tracing lines (H2 and [Fe II]) to examine physical properties and kinematics of the object. Results. A large increase in luminosity was found between the 2005 and 2013 epochs of more than 1 magnitude in the K band, followed in 2014 by a steep decrease. Consistently, the mass accretion rate (Ṁacc) rose by an order of magnitude from ∼10−8 M⊙ yr−1 to ∼10−7 M⊙ yr−1 between the two early epochs. The visual extinction (AV) has also increased from ∼15 mag in 2005 to ∼24 mag in 2013. This rise in AV in tandem with the increase in Ṁacc is explained by the lifting up of a large amount of dust from the disc of IRS 54, following the augmented accretion and ejection activity in the YSO, which intersects our line of sight due to the almost edge-on geometry of the disc. Because of the strength and timescales involved in this dramatic increase, this event is believed to have been an accretion burst possibly similar to bursts of EXor-type objects. IRS 54 is the lowest mass Class I source observed to have an accretion burst of this type, and therefore potentially one of the lowest mass EXor-type objects known so far.

Rotational excitation of highly excited H2O by H2

2021 ◽  
Vol 502 (4) ◽  
pp. 5356-5361
Author(s):  
Michal Żóltowski ◽  
François Lique ◽  
Agata Karska ◽  
Piotr S Żuchowski
Keyword(s):  
Energy Levels ◽  
Radiative Properties ◽  
Rate Coefficients ◽  
Young Stellar Objects ◽  
Stellar Objects ◽  
Excitation Rate ◽  
Physical Conditions ◽  
James Webb Space Telescope ◽  
Non Local ◽  
Insight Into

ABSTRACT Water is a key molecule for interstellar chemistry. Observations with Herschel telescope show significant population of very high rotational transitions (j ≳ 8) in young stellar objects, indicating significant amounts of water in hot (T ≳ 1500 K) and dense (n ≳ 106 cm−3) gas. Non-local thermodynamic equilibrium (LTE) modelling of these observations requires the knowledge of the collisional and radiative properties of highly excited water at high temperature. The aim of this work is to calculate a new set of excitation rate coefficients for both para- and ortho-H2O induced by collisions with H2 for energy levels up to j = 17. Quantum scattering calculations were performed using a reduced dimensional approach and the coupled states approximation. Rate coefficients were obtained for 97 pure rotational energy levels of both para- and ortho-H2O and for temperatures up to 2000 K. With the forthcoming launch of the James Webb Space Telescope, these new collisional data will allow us to gain more insight into the physical conditions in star- and planet-forming regions.

Stellar populations in the BAaDE survey

2019 ◽  
Vol 14 (S353) ◽  
pp. 43-44
Author(s):  
Megan O. Lewis ◽  
Ylva M. Pihlström ◽  
Loránt O. Sjouwerman ◽  
Michael C. Stroh ◽  
Keyword(s):  
Detection Rate ◽  
Galactic Plane ◽  
Dynamical Evolution ◽  
Stellar Populations ◽  
Young Stellar Objects ◽  
Line Of Sight ◽  
Stellar Objects ◽  
Evolved Stars ◽  
Color Identification ◽  
Infrared Sources

AbstractThe BAaDE (Bulge Asymmetries and Dynamical Evolution) project is an SiO maser survey of the Galactic Plane. About 19,000 sources have been observed at 43 GHz with the VLA, and the production of spectra for each of these sources is well underway. The primary goal of the project is to collect line-of-sight velocities for all the detected masers in the sample to probe Galactic dynamics. With an expected detection rate of over 60% we should collect over 11,000 velocities to probe the Galactic potential. The survey is also a large sample of infrared sources to explore the different evolved stellar populations within the Milky Way. So far we discern three distinct groups in the BAaDE sample: the main group containing oxygen-rich, evolved stars with a high SiO maser detection rate, a much smaller population of carbon-rich evolved stars, and finally a group of likely young stellar objects with no maser emission. These populations are separated using 2MASS and MSX color-color diagrams, and we find a particularly useful cut between the young and evolved objects using the MSX [D] –[E] color. Identification of these populations will isolate BAaDE’s evolved star sample, and will more tightly define the region in IR color-color diagrams where SiO masers occur yielding a better understanding of these kinematical probes. Using our color-divisions we can also study the distribution of each of the populations within the Galactic Plane.

A Near-Infrared Search for Companions around Very Low Luminosity Young Stellar Objects in Taurus

1999 ◽  
Vol 117 (3) ◽  
pp. 1471-1484 ◽  
Author(s):  
Yoichi Itoh ◽  
Motohide Tamura ◽  
Tadashi Nakajima
Keyword(s):  
Near Infrared ◽  
Young Stellar Objects ◽  
Stellar Objects
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