scholarly journals Outflow activity in brown dwarfs

2007 ◽  
Vol 3 (S243) ◽  
pp. 357-364
Author(s):  
Emma T. Whelan ◽  
Thomas P. Ray ◽  
Francesca Bacciotti ◽  
Sofia Randich ◽  
Ray Jayawardhana ◽  
...  
Keyword(s):  
Spatial Information ◽  
Ambient Medium ◽  
Brown Dwarfs ◽  
Emission Lines ◽  
Young Stellar Objects ◽  
Brown Dwarf ◽  
Stellar Objects ◽  
Novel Technique ◽  
Driving Source ◽  
Future Plans

AbstractWhile numerous studies have been aimed at understanding the properties of young brown dwarfs relatively little exploration of their potential as drivers of outflows has occurred. Forbidden emission lines are important probes of outflows from young stellar objects, as they trace the shocks which form as an outflow interacts with the ambient medium of its driving source. While forbidden emission was identified in the spectra of young brown dwarfs, indicating the presence of outflows, these lines were weak and confined to the brown dwarf continuum position. Hence their origin in an outflow could not be confirmed. Our approach to this problem, is to analyse the forbidden line regions of brown dwarfs using spectro-astrometry. Spectro-astrometry is a novel technique which allows the user to recover spatial information from a spectrum beyond the limitations of the seeing of the observation. Using this technique we have found two brown dwarf outflows to date. In this chapter we outline this technique, describe our results for the brown dwarfs ρ-Oph 102 and 2MASS1207-3932 and discuss our future plans.

scholarly journals Considerations for atmospheric retrieval of high-precision brown dwarf spectra

2020 ◽  
Vol 497 (4) ◽  
pp. 5136-5154
Author(s):  
Anjali A A Piette ◽  
Nikku Madhusudhan
Keyword(s):  
High Precision ◽  
Thermal Emission ◽  
Simulated Data ◽  
Brown Dwarfs ◽  
High Signal ◽  
Temperature Structure ◽  
Wide Field ◽  
Brown Dwarf ◽  
Data Set ◽  
Stellar Objects

ABSTRACT Isolated brown dwarfs provide remarkable laboratories for understanding atmospheric physics in the low-irradiation regime, and can be observed more precisely than exoplanets. As such, they provide a glimpse into the future of high-signal-to-noise ratio (SNR) observations of exoplanets. In this work, we investigate several new considerations that are important for atmospheric retrievals of high-quality thermal emission spectra of sub-stellar objects. We pursue this using an adaptation of the h y dra atmospheric retrieval code. We propose a parametric pressure–temperature (P–T) profile for brown dwarfs consisting of multiple atmospheric layers, parametrized by the temperature change across each layer. This model allows the steep temperature gradient of brown dwarf atmospheres to be accurately retrieved while avoiding commonly encountered numerical artefacts. The P–T model is especially flexible in the photosphere, which can reach a few tens of bar for T-dwarfs. We demonstrate an approach to include model uncertainties in the retrieval, focusing on uncertainties introduced by finite spectral and vertical resolution in the atmospheric model used for retrieval (∼8 per cent in the present case). We validate our retrieval framework by applying it to a simulated data set and then apply it to the HST/WFC3 (Hubble Space Telescope’s Wide-Field Camera 3) spectrum of the T-dwarf 2MASS J2339+1352. We retrieve sub-solar abundances of H2O and CH4 in the object at ∼0.1 dex precision. Additionally, we constrain the temperature structure to within ∼100 K in the photosphere. Our results demonstrate the promise of high-SNR spectra to provide high-precision abundance estimates of sub-stellar objects.

scholarly journals Validating post-AGB candidates in the LMC and SMC using SALT spectra

2020 ◽  
Vol 641 ◽  
pp. A142
Author(s):  
R. Szczerba ◽  
M. Hajduk ◽  
Ya. V. Pavlenko ◽  
B. J. Hrivnak ◽  
B. M. Kaminsky ◽  
...  
Keyword(s):  
South African ◽  
Stellar Atmosphere ◽  
Magellanic Clouds ◽  
Emission Lines ◽  
Young Stellar Objects ◽  
Agb Stars ◽  
Large Telescope ◽  
Stellar Objects ◽  
Effective Temperatures ◽  
The Continuum

We selected a sample of post-AGB candidates in the Magellanic Clouds on the basis of their near- and mid-infrared colour characteristics. Fifteen of the most optically bright post-AGB candidates were observed with the South African Large Telescope in order to determine their stellar parameters and thus to validate or discriminate their nature as post-AGB objects in the Magellanic Clouds. The spectral types of absorption-line objects were estimated according to the MK classification, and effective temperatures were obtained by means of stellar atmosphere modelling. Emission-line objects were classified on the basis of the fluxes of the emission lines and the presence of the continuum. Out of 15 observed objects, only 4 appear to be genuine post-AGB stars (27%). In the SMC, 1 out of 4 is post-AGB, and in the LMC, 3 out 11 are post-AGB objects. Thus, we can conclude that the selected region in the colour-colour diagram, while selecting the genuine post-AGB objects, overlaps severely with other types of objects, in particular young stellar objects and planetary nebulae. Additional classification criteria are required to distinguish between post-AGB stars and other types of objects. In particular, photometry at far-IR wavelengths would greatly assist in distinguishing young stellar objects from evolved ones. On the other hand, we showed that the low-resolution optical spectra appear to be sufficient to determine whether the candidates are post-AGB objects.

Two New T Tauri stars and a Candidate FU Orionis Star associated with Bok Globules

1997 ◽  
Vol 163 ◽  
pp. 839-839
Author(s):  
J. L. Yun ◽  
M. Moreira
Keyword(s):  
Infrared Emission ◽  
T Tauri Stars ◽  
Emission Lines ◽  
Young Stellar Objects ◽  
Spectral Energy ◽  
Energy Distributions ◽  
Stellar Objects ◽  
T Tauri ◽  
Bok Globules ◽  
Reflection Nebulae

AbstractWe present photometric and spectroscopic evidence of two new T Tauri stars formed in the conditions of isolated small Bok globules. The spectral energy distributions of these objects display excess infrared emission, they are associated with optical reflection nebulae, and their optical spectra reveal Balmer emission lines and the Li I λ6707 Å absorption line. Additionnally, we report the discovery of what is likely to be a new FU Orionis star seen towards Bok globule CB34. The star is about 4 magnitudes brighter than it appears on the Palomar plates and is associated with the aggregate of young stellar objects forming in Bok globule CB34.

scholarly journals Characterising the Protostellar Population of the Magellanic Clouds with VLT/SINFONI

2015 ◽  
Vol 11 (S315) ◽  
Author(s):  
Jacob Ward ◽  
Joana Oliveira ◽  
Jacco van Loon ◽  
Marta Sewilo
Keyword(s):  
Star Formation ◽  
Milky Way ◽  
Large Magellanic Cloud ◽  
Magellanic Cloud ◽  
Magellanic Clouds ◽  
Emission Lines ◽  
Young Stellar Objects ◽  
Small Magellanic Cloud ◽  
Stellar Objects ◽  
Accretion Rates

AbstractAt distances of ~50 kpc and ~60 kpc for the Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC) respectively the Magellanic Clouds present us with a unique opportunity to study star formation in environments outside our own galaxy. Through Spitzer and Herschel photometry and spectroscopy, samples of Young Stellar Objects (YSOs) have been selected and spectroscpically confirmed in the Magellanic Clouds. Here we present some of the key results of our SINFONI K-band observations towards massive YSOs in the Magellanic Clouds. We resolve a number of Spitzer sources into multiple, previously unresolved, components and our analysis of emission lines suggest higher accretion rates and different disc properties compared with massive YSOs in the Milky Way.

scholarly journals Photometric and spectroscopic studies of very low mass YSOs and young Brown Dwarfs in S106

2006 ◽  
Vol 2 (S237) ◽  
pp. 457-457
Author(s):  
Yumiko Oasa
Keyword(s):  
Massive Star ◽  
Near Infrared ◽  
Brown Dwarfs ◽  
Spectroscopic Studies ◽  
Young Stellar Objects ◽  
Stellar Objects ◽  
Hii Region ◽  
Star Forming ◽  
Star Forming Regions ◽  
Low Mass

Young brown dwarfs have been identified in a significant population in various star forming regions. Some deep surveys have yielded less massive objects with planetary-mass (e.g., Oasa et al. 1999; Lucas & Roche 2000). Nevertheless, it is not yet clear how abundant these very low-mass objects are formed. S106 is one of the nearest massive star-forming regions associated with prominent bipolar nebulae and an HII region. We have conducted near-infrared photometric and spectroscopic observations of very low-mass young stellar objects (YSOs) in the S106 region.

scholarly journals High Angular Resolution Observations of Maser Kinematics Near Low Mass Young Stellar Objects

2001 ◽  
Vol 205 ◽  
pp. 256-257
Author(s):  
Kevin B. Marvel ◽  
Mark Claussen ◽  
H. Alwyn Wootten ◽  
Bruce Wilking
Keyword(s):  
Angular Resolution ◽  
Surrounding Medium ◽  
Young Stellar Objects ◽  
High Angular Resolution ◽  
Stellar Objects ◽  
Star Forming ◽  
Low Mass ◽  
Water Masers ◽  
Driving Source ◽  
Water Maser

With the advent of new correlators and dedicated arrays, spectral line VLBI is entering its ascendancy as a probe of a variety of interesting astrophysical environments. One of the most interesting environments where spectroscopic VLBI techniques are valuable are the regions directly coincident with forming stars. In these sources, water maser emission is observed when the outflowing jets of material interact with the surrounding medium. Observations of these water masers dramatically reveal the innermost regions of the star formation process at or below the 1-AU scale.We have found that the water masers clearly trace the jets at these scales. The masers show space motions on the order of 60 to 100 kms−1 and form within a few AU of the exciting protostar. By observing the distributions and motions of the water masers associated with these objects, we may be able to address in greater detail the collimation mechanism of the jets seen in these protostars.In this brief poster proceeding, we provide a summary image of the water masers associated with SVS13, the driving source for the HH 7-11 objects. We have also mapped the masers associated with IRAS 16293-2422, IRAS 05413-0104, IRAS 4A and IRAS 4B, both in the NGC 1333 star forming region. For further information on these sources, please contact any of the authors directly.

scholarly journals A Search for Water Maser Emission from Brown Dwarfs and Low-luminosity Young Stellar Objects

2017 ◽  
Vol 153 (5) ◽  
pp. 221
Author(s):  
José F. Gómez ◽  
Aina Palau ◽  
Lucero Uscanga ◽  
Guillermo Manjarrez ◽  
David Barrado
Keyword(s):  
Brown Dwarfs ◽  
Young Stellar Objects ◽  
Stellar Objects ◽  
Maser Emission ◽  
Water Maser
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