Detection of Photospheric Features in the Near-infrared Spectrum of a Class 0 Protostar

Greene, Thomas P.; Gully-Santiago, Michael; Barsony, M.

doi:10.3847/1538-4357/aacc6c

Cited by 17 publications

(26 citation statements)

References 38 publications

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“…By assuming a typical reddening as A V = 20 mag and R V = 3.1, these flux ratios will be increased by 17% after de-reddening. This result rules out the possibility of pure UV excitation, similar to a recent measurement of a Class 0 protostar (S68N; Greene et al 2018). This method is also applied to other three objects (v20, v473 and v699) which have detectable H 2 2 -1 S(1) lines.…”

Section: V815: Launching Of Outflow On a Short Timescalesupporting

confidence: 80%

Short- and long-term near-infrared spectroscopic variability of eruptive protostars from VVV

Guo

Lucas

Peña

et al. 2019

Monthly Notices of the Royal Astronomical Society

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Numerous eruptive variable young stellar objects (YSOs), mostly Class I systems, were recently detected by the near-infrared Vista Variables in the Via Lactea (VVV) survey. We present an exploratory near-infrared spectroscopic variability study of 14 eruptive YSOs. The variations were sampled over 1-day and 1 to 2-year intervals and analysed in combination with VVV light curves. CO overtone absorption features are observed on 3 objects with FUor-like spectra: all show deeper absorption when they are brighter. This implies stronger emission from the circumstellar disc with a steeper vertical temperature gradient when the accretion rate is higher. This confirms the nature of fast VVV FUor-like events, in line with the accepted picture for classical FUors. The absence of Brγ emission in a FUor-like object declining to pre-outburst brightness suggests that reconstruction of the stellar magnetic field is a slow process. Within the 1-day timescale, 60% of H 2 -emitting YSOs show significant but modest variation, and 2/6 sources have large variations in Brγ. Over year-long timescales, H 2 flux variations remain modest despite up to 1.8 mag variation in K s . This indicates that emission from the molecular outflow usually arises further from the protostar and is unaffected by relatively large changes in accretion rate on year-long timescales. Two objects show signs of on/off magnetospheric accretion traced by Brγ emission. In addition, a 60% inter-night brightening of the H 2 outflow is detected in one YSO.

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Section: V815: Launching Of Outflow On a Short Timescalesupporting

confidence: 80%

Short- and long-term near-infrared spectroscopic variability of eruptive protostars from VVV

Guo

Lucas

Peña

et al. 2019

Monthly Notices of the Royal Astronomical Society

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“…There have been few other Class 0s that have had their near-IR spectroscopic observations analyzed for both emission and absorption components. Serpens S68N also exhibited H 2 emission but was absent in Br γ and showed CO bands in absorption rather than emission (Greene et al 2018). We report the incidence rates of these features in emission among our 5 continuumdetected Class 0s (Figure 1) and Serpens S68N in Table 5.…”

Section: 2mentioning

confidence: 79%

“…At a disk accretion rate of ∼10 −6 M yr −1 , a protostar can sustain a stellar magnetosphere (and produce the Br γ line profiles we observe) if it has developed a strong, organized stellar magnetic field. If our Class 0 sources have a protostellar mass of 0.2 M (as measured for the similarly low-luminosity Class 0 source L1527 IRS; Tobin et al 2012) and a stellar surface gravity (log g) of 2.38 (as measured for Serpens S68N; Greene et al 2018), protostellar radii are ∼4-5 R . If the Class 0 sources further have a disk accretion of ∼10 −6 M yr −1 and their stellar magnetospheres truncate the inner disk at ∼2 stellar radii (as measured for the Class I YLW 15; Greene & Lada 2002), the required protostellar magnetic field strength is ∼1 kG (Hartmann et al 2016 and references therein).…”

Section: 2mentioning

confidence: 81%

“…An accretion level of this magnitude could plausibly suppress the stellar magnetosphere, explaining the absence of Br γ, while still remaining below an FU Ori accretion level, allowing for CO emission (rather than absorption). As a variant in a different direction, the recent near-IR spectrum of Serpens S68N lacks Br γ emission and exhibited CO bands in absorption (Greene et al 2018). Serpens S68N is likely in a state of lower disk accretion than our Class 0s, with low veiling indicated by its observed photospheric absorption features (Na I, Ca I).…”

Section: 2mentioning

confidence: 99%

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The Near Stellar Environment of Class 0 Protostars: A First Look with Near-Infrared Spectroscopy

Laos,

Greene,

Najita

et al. 2021

Preprint

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We present near-infrared K -band spectra for a sample of 7 Class 0 protostars in the Perseus and Orion star-forming regions. We detect Br γ, CO overtone, and H 2 emission, features that probe the near circumstellar environment of the protostar and reveal evidence of magnetospheric accretion, a hot inner disk atmosphere, and outflows, respectively. Comparing the properties of these features with those of Class I sources from the literature, we find that their Br γ and CO emission are generally consistent in strength and velocity width. The Br γ line profiles are broad and centrally peaked, with FWHMs of ∼200 km s −1 and wings extending to ∼300 km s −1 . The line ratios of our H 2 emission features, which are spatially extended for some sources, are consistent with shock excitation and indicate the presence of strong jets or a disk wind. Within our small sample, the frequency of CO band emission (∼67%) is high relative to that of Class I samples (∼15%), indicating that Class 0s have high inner disk accretion rates, similar to those of the most actively accreting Class I sources. Collectively, our results suggest that Class 0 sources have similar accretion mechanisms to the more evolved classes, with strong organized stellar magnetic fields established at the earliest observable stage of evolution.

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“…A list of research groups working on this issue can be found in Dumusque et al (2017) and in Nelson et al (2020). MCMC are also used in spectroscopic studies (Greene et al 2018;Casasayas-Barris et al 2020).…”

Section: Introductionmentioning

confidence: 99%

A Bayesian inference and model selection algorithm with an optimisation scheme to infer the model noise power

Lopez-Santiago,

Martino,

Miguez

et al. 2021

Preprint

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Model fitting is possibly the most extended problem in science. Classical approaches include the use of least-squares fitting procedures and maximum likelihood methods to estimate the value of the parameters in the model. However, in recent years, Bayesian inference tools have gained traction. Usually, Markov chain Monte Carlo methods are applied to inference problems, but they present some disadvantages, particularly when comparing different models fitted to the same dataset. Other Bayesian methods can deal with this issue in a natural and effective way. We have implemented an importance sampling algorithm adapted to Bayesian inference problems in which the power of the noise in the observations is not known a priori. The main advantage of importance sampling is that the model evidence can be derived directly from the so-called importance weights -while MCMC methods demand considerable postprocessing. The use of our adaptive target, adaptive importance sampling (ATAIS) method is shown by inferring, on the one hand, the parameters of a simulated flaring event which includes a damped oscillation and, on the other hand, real data from the Kepler mission. ATAIS includes a novel automatic adaptation of the target distribution. It automatically estimates the variance of the noise in the model. ATAIS admits parallelisation, which decreases the computational run-times notably. We compare our method against a nested sampling method within a model selection problem.

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Detection of Photospheric Features in the Near-infrared Spectrum of a Class 0 Protostar

Cited by 17 publications

References 38 publications

Short- and long-term near-infrared spectroscopic variability of eruptive protostars from VVV

Short- and long-term near-infrared spectroscopic variability of eruptive protostars from VVV

The Near Stellar Environment of Class 0 Protostars: A First Look with Near-Infrared Spectroscopy

A Bayesian inference and model selection algorithm with an optimisation scheme to infer the model noise power

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