X-shooter observations of low-mass stars in the<i>η</i>Chamaeleontis association

Rugel, M.; Fedele, D.; Herczeg, Gregory J.

doi:10.1051/0004-6361/201630111

Cited by 39 publications

(49 citation statements)

References 77 publications

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“…The equivalent width of Hα can vary by up to factors of a few in CTTS and up to ×2 in WTTS (e.g. Rugel et al 2018). Therefore, a star classified as CTTS in one observation may be deemed as a WTTS at some other epoch.…”

Section: Classification Of Accreting and Non-accretingmentioning

confidence: 99%

The CIDA Variability Survey of Orion OB1. II. Demographics of the Young, Low-mass Stellar Populations^*

et al. 2019

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We present results of our large scale, optical, multi-epoch photometric survey of ∼ 180 square degrees across the Orion OB1 association, complemented with extensive follow up spectroscopy. Our focus is mapping and characterizing in an uniform way the off-cloud, low-mass, pre-main sequence populations. We report 2064, mostly K and M-type, confirmed T Tauri members. Most (59%) are located in the OB1a subassociation, 27% are projected onto the OB1b subassociation, and the remaining 14% are located within the confines of the A and B molecular clouds. There is significant structure in the spatial distribution of the young stars. We characterize two new clusterings of T Tauri stars, the HD 35762 and HR 1833 groups, both located in the OB1a subassociation, not far form the 25 Ori cluster. We also confirm two stellar overdensities in OB1b, I and II, containing a total of 231 T Tauri stars. A ∼ 2 deg wide halo of young stars surrounds the Orion Nebula Cluster; the north and south parts corresponding to the low-mass populations of NGC 1977 and NGC 1980, respectively. There is indication of two populations of young stars in the OB1b region, located at two different distances, which may be due to the OB1a subassociation overlapping on front of OB1b. The various groups and regions can be ordered in an age sequence that agrees with the long standing picture of star formation starting in Orion OB1a some 10-15 Myr ago.We use the strength of the Hα line in emission, combined with characteristics of IR excesses and optical variability, to define a new type of T Tauri star, the C/W class, stars we propose may be nearing the end of their accretion phase, in an evolutionary state between that of Classical T Tauri and Weak-lined T Tauri stars. The evolution of the ensemble-wide equivalent width of the Li Iλ6707 line shows the depletion of Li with a timescale of 8.5 Myr. The decline of the accretion fraction, from ∼ 2 − 10 Myr, implies an accretion e-folding timescale of 2.1 Myr, consistent with previous studies. Finally, we use the median amplitude of the V -band variability in each type of star, to show the decline of stellar activity, from the accreting Classical T Tauri stars to the population of least active field dwarfs.

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Section: Classification Of Accreting and Non-accretingmentioning

confidence: 99%

The CIDA Variability Survey of Orion OB1. II. Demographics of the Young, Low-mass Stellar Populations^*

et al. 2019

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“…We perform spectral classification of the normalized spectra by fitting them with two sets of spectral templates: one collected from the Very Large Telescope/X-shooter for pre-main-sequence (PMS) stars with spectral types ranging from G6 to M9.5 (Manara et al 2013(Manara et al , 2017Rugel et al 2018; see also Fang et al 2020) and the other from a combination of model atmospheres with T eff = 2775-35,000 K, surface gravity logg=3.5-5, and v sini= 0-150 km s −1 with models for T eff =2775-12,000 K from Husser et al (2013) and for T eff above 12,000 K from Mészáros et al (2012). For the X-shooter templates, we interpolate them into two sets for use as described below, one with a grid spacing of 1.0 spectral subclass and the other with a grid spacing of 0.2 spectral subclasses.…”

Section: Spectral Classificationmentioning

confidence: 99%

The First Extensive Spectroscopic Study of Young Stars in the North America and Pelican Nebulae

Fang

Hillenbrand

Kim

et al. 2020

ApJ

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We present a spectroscopic survey of over 3400 potential members in the North America and Pelican Nebulae (NAP) using several low-resolution (R≈1300-2000) spectrographs: Palomar/Norris, WIYN/Hydra, Keck/DEep Imaging Multi-Object Spectrograph (DEIMOS), and the Multiple Mirror Telescope (MMT)/Hectospec. We identify 580 young stars as likely members of the NAP region based on criteria involving infrared excess, Li I 6708 Å absorption, X-ray emission, parallax, and proper motions. The spectral types of individual spectra are derived by fitting them with templates that are either empirical spectra of pre-main-sequence stars or model atmospheres. The templates are artificially veiled, and a best-fit combination of spectral type and veiling parameter is derived for each star. We use the spectral types with archival photometry to derive V-band extinction and stellar luminosity. From the Hertzsprung-Russell diagram, the median age of the young stars is about 1 Myr, with a luminosity dispersion of ∼0.3-0.4 dex. We investigate the photometric variability of the spectroscopic member sample using Zwicky Transient Facility data and conclude that photometric variability, while present, does not significantly contribute to the luminosity dispersion. While larger than the formal errors, the luminosity dispersion is smaller than if veiling were not taken into account in our spectral typing process. The measured ages of the stellar kinematic groups, combined with the inferred ages for embedded stellar populations revealed by Spitzer, suggest a sequential history of star formation in the NAP region.

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“…JW847 was classified as a K6, and for that reason we should be cautious when using this criterion, since this is not an M-type star. Although this criterion should be valid for mid-M dwarfs, Rugel et al (2018) used this criterion from K6 to M6 type stars belonging to the η Chamaeleontis association.…”

Section: Balmer Continuum and Emission Linesmentioning

confidence: 99%

Accretion in low-mass members of the Orion Nebula Cluster with young transition disks

Albuquerque

Gameiro

Alencar

et al. 2020

A&A

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Context. Although the Orion Nebula Cluster is one of the most studied clusters in the solar neighborhood, the evolution of the very low-mass members (M * < 0.25 M ) has not been fully addressed due to their faintness. Aims. Our goal is to verify if some young and very low-mass objects in the Orion Nebula Cluster show evidence of ongoing accretion using broadband VLT/X-Shooter spectra. Methods. For each target, we determined the corresponding stellar parameters, veiling, observed Balmer jump, and accretion rates. Additionally, we searched for the existence of circumstellar disks through available on-line photometry. Results. We detected accretion activity in three young stellar objects in the Orion Nebula Cluster, two of them being in the very low-mass range. We also detected the presence of young transition disks with ages between 1 and 3.5 Myr.

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X-shooter observations of low-mass stars in theηChamaeleontis association

Cited by 39 publications

References 77 publications

The CIDA Variability Survey of Orion OB1. II. Demographics of the Young, Low-mass Stellar Populations^*

The CIDA Variability Survey of Orion OB1. II. Demographics of the Young, Low-mass Stellar Populations^*

The First Extensive Spectroscopic Study of Young Stars in the North America and Pelican Nebulae

Accretion in low-mass members of the Orion Nebula Cluster with young transition disks

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X-shooter observations of low-mass stars in theηChamaeleontis association

Cited by 39 publications

References 77 publications

The CIDA Variability Survey of Orion OB1. II. Demographics of the Young, Low-mass Stellar Populations*

The CIDA Variability Survey of Orion OB1. II. Demographics of the Young, Low-mass Stellar Populations*

The First Extensive Spectroscopic Study of Young Stars in the North America and Pelican Nebulae

Accretion in low-mass members of the Orion Nebula Cluster with young transition disks

Contact Info

Product

Resources

About

The CIDA Variability Survey of Orion OB1. II. Demographics of the Young, Low-mass Stellar Populations^*

The CIDA Variability Survey of Orion OB1. II. Demographics of the Young, Low-mass Stellar Populations^*