Puzzling fluorescent emission from Orion

Czesla, S.; Schmitt, J. H. M. M.

doi:10.1051/0004-6361/201014706

Cited by 12 publications

(11 citation statements)

References 35 publications

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“…The test statistic is −2∆ ln L. According to Wilk's theorem (Wilks 1938), the probability distribution of the test statistic can be approximated by a χ 2 distribution with d f degrees of freedom for large data samples. However, as discussed by Protassov et al (2002), Baluev (2009), and Czesla & Schmitt (2010), the formal criteria for this approximation are not fulfilled in the current case. While the models are nested as required, the circular single-planet model is only obtained from our elliptical or two-planet models by choosing parameters at the edge of the parameter space such as zero eccentricity.…”

Section: Likelihood Analysismentioning

confidence: 75%

The CARMENES search for exoplanets around M dwarfs

Nagel

Czesla

Schmitt

et al. 2019

A&A

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We report the detection of a Neptune-mass exoplanet around the M4.0 dwarf GJ 4276 (G 232-070) based on radial velocity (RV) observations obtained with the CARMENES spectrograph. The RV variations of GJ 4276 are best explained by the presence of a planetary companion that has a minimum mass of m b sin i ≈ 16 M ⊕ on a P b = 13.35 day orbit. The analysis of the activity indicators and spectral diagnostics exclude stellar induced RV perturbations and prove the planetary interpretation of the RV signal. We show that a circular single-planet solution can be excluded by means of a likelihood ratio test. Instead, we find that the RV variations can be explained either by an eccentric orbit or interpreted as a pair of planets on circular orbits near a period ratio of 2:1. Although the eccentric single-planet solution is slightly preferred, our statistical analysis indicates that none of these two scenarios can be rejected with high confidence using the RV time series obtained so far. Based on the eccentric interpretation, we find that GJ 4276 b is the most eccentric (e b = 0.37) exoplanet around an M dwarf with such a short orbital period known today.

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Section: Likelihood Analysismentioning

confidence: 75%

The CARMENES search for exoplanets around M dwarfs

Nagel

Czesla

Schmitt

et al. 2019

A&A

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“…is less energetically challenging (Czesla & Schmitt 2010). The plasma temperature is not well constrained mainly due to the low count rate, but a hot plasma temperature is favored (kT = 4.1 +13.8 −2.8 keV), which is consistent with a magnetic flare and the photoionization of iron.…”

Section: X-ray Flare Spectrummentioning

confidence: 99%

“…The neutral iron can be ionized by photons or electrons that have energies larger than the Fe K-shell ionization potential of 7.112 keV. The contributions of these two ionization channels to the observed X-ray line in accreting young stars and Class I protostars (Güdel & Nazé 2009;Hamaguchi et al 2005Hamaguchi et al , 2010Czesla & Schmitt 2010;Pillitteri et al 2019) Fig. 3.…”

Section: X-ray Flare Spectrummentioning

confidence: 99%

Evidence for magnetic activity at starbirth: a powerful X-ray flare from the Class 0 protostar HOPS 383

Grosso

Hamaguchi

Principe

et al. 2020

A&A

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Context. Class 0 protostars represent the earliest evolutionary stage of solar-type stars, during which the majority of the system mass resides in an infalling envelope of gas and dust and is not yet in the central, nascent star. Although X-rays are a key signature of magnetic activity in more evolved protostars and young stars, whether such magnetic activity is present at the Class 0 stage is still debated. Aims. We aim to detect a bona fide Class 0 protostar in X-rays. Methods. We observed HOPS 383 in 2017 December in X-rays with the Chandra X-ray Observatory (∼84 ks) and in near-infrared imaging with the Southern Astrophysical Research telescope. Results. HOPS 383 was detected in X-rays during a powerful flare. This hard (E > 2 keV) X-ray counterpart was spatially coincident with the northwest 4 cm component of HOPS 383, which would be the base of the radio thermal jet launched by HOPS 383. The flare duration was ∼3.3 h; at the peak, the X-ray luminosity reached ∼4 × 1031 erg s−1 in the 2−8 keV energy band, a level at least an order of magnitude larger than that of the undetected quiescent emission from HOPS 383. The X-ray flare spectrum is highly absorbed (NH ∼ 7 × 1023 cm−2), and it displays a 6.4 keV emission line with an equivalent width of ∼1.1 keV, arising from neutral or low-ionization iron. Conclusions. The detection of a powerful X-ray flare from HOPS 383 constitutes direct proof that magnetic activity can be present at the earliest formative stages of solar-type stars.

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“…This result makes unrealistic a simple model made of an irradiated disk, and hints that other mechanisms of reverberation and/or a more complex geometry that takes into account the cavity where Elias 29 sits can have a role for explaining such high EWs. Fe fluorescence in YSOs of ONC has been investigated by Czesla & Schmitt (2010), they remarked how explaining the origin of the fluorescent line at 6.4 keV in a few case of quiescent sources is still an open issue. Their sample of COUP sources span a range of N H in 2 × 10 20 − 2 × 10 23 cm −2 and EWs between ∼ 0.1 and 0.8 keV (including the quoted uncertainties), with the only exception of V 1486 Ori (COUP # 331) which showed EW≥ 1.4 keV.…”

Section: Discussionmentioning

confidence: 99%

Deep X-ray view of the Class I YSO Elias 29 with XMM-Newton and NuSTAR

Pillitteri

Sciortino

Reale

et al. 2019

A&A

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X-ray emission is a characteristic feature of young stellar objects (YSOs) and the result of the interplay between rotation, magnetism and accretion. For this reason high energy phenomena are key elements to understand the process of star formation, the evolution of their circumstellar disks and eventually the formation of planets. We investigated the X-ray characteristics of the Class I YSO Elias 29 with joint XMM-Newton and NuSTAR observations of total duration 300 ks and 450 ks, respectively. These are the first observations of a very young (< 1 Myr) stellar object in a band encompassing simultaneously both soft and hard X-rays (0.3 − 10 keV in XMM-Newton, and ≈ 3 − 80 keV in NuSTAR). The quiescent spectrum is well described by one thermal component at ∼ 4.2 keV absorbed by N H ∼ 5.5 × 10 22 cm −2 . In addition to the hot Fe complex at 6.7 keV, we observed fluorescent emission from Fe at ∼ 6.4 keV, confirming the previous findings. The line at 6.4 keV is detected during quiescent and flaring states and its flux is variable. The equivalent width is found varying in the ≈ 0.15 − −0.5 keV range. These values make unrealistic a simple model with a centrally illuminated disk and suggest a role of the cavity containing Elias 29 and possibly reverberation processes that could occur in it. We observed two flares, with duration of 20 ks and 50 ks, respectively but only the first flare was observed with both XMM-Newton and NuSTAR. For this flare, we used its peak temperature and timing as diagnostics to infer a loop size of about 1 − 2R in length, which is about 20% − 30% of the stellar radius. This implies a relatively compact structure. We systematically observed an increase of N H during the flares of a factor five. This behavior has been observed during flares previously detected in Elias 29 with XMM-Newton and ASCA. The phenomenon hints that the flaring regions could be buried under the accretion streams and at high stellar latitudes, as the X-rays from flares pass through gas denser than the gas along the line of sight of the quiescent corona. In a different scenario, a contribution from scattered soft photons to the primary coronal emission could mimic a shallower N H in the quiescent spectrum. In the spectrum of the full NuSTAR exposure, we detect hard X-ray emission in the band ≈ 20 − 80 keV in excess with respect to the thermal emission and significant at a level of ≥ 2σ. We speculate that the hard X-ray emission could be due to a population of energetic electrons accelerated by the magnetic field along the accretion streams. These particles could concur to pumping up the Fe fluorescence when hitting cold Fe of the circumstellar disk along with X-ray photons with E > 7.11 keV.

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Puzzling fluorescent emission from Orion

Cited by 12 publications

References 35 publications

The CARMENES search for exoplanets around M dwarfs

The CARMENES search for exoplanets around M dwarfs

Evidence for magnetic activity at starbirth: a powerful X-ray flare from the Class 0 protostar HOPS 383

Deep X-ray view of the Class I YSO Elias 29 with XMM-Newton and NuSTAR

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