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![I − J versus J −[3.6] colour-colour diagram of the X-ray sources of NGC 2023. The continuous line represents the ZAMS and the dashed line is the 1 Myr isochrone (Baraffe et al. 1998). The shaded region is the locus of quasars (adapted from Barrado et al. 2011). Symbols are the same as in Fig. 3. The extinction vector is A V = 1.5 mag.](profile/J-Lopez-Santiago/publication/233399056/figure/fig6/AS:669665395220498@1536672080699/I-J-versus-J-36-colour-colour-diagram-of-the-X-ray-sources-of-NGC-2023-The.png)
I − J versus J −[3.6] colour-colour diagram of the X-ray sources of NGC 2023. The continuous line represents the ZAMS and the dashed line is the 1 Myr isochrone (Baraffe et al. 1998). The shaded region is the locus of quasars (adapted from Barrado et al. 2011). Symbols are the same as in Fig. 3. The extinction vector is A V = 1.5 mag.
Source publication
Nearby star-forming regions are ideal laboratories to study high-energy emission of different stellar populations, from very
massive stars to brown dwarfs. NGC 2023 is a reflection nebula situated to the south of the Flame Nebula (NGC 2024) and at
the edge of the H ii region IC 434, which also contains the Horsehead Nebula (Barnard 33). NGC 2023, N...
Contexts in source publication
Context 1
... results are given in Table A2. These will be discussed and compared with those obtained from spectral energy distribution (SED) fitting in Section 3.4. Barrado et al. (2011) showed that the I − J versus J −[3.6] colour-colour diagram can be used to reject extragalactic objects from X-ray selected samples, as AGNs are well separated from stars. Fig. 5 shows the same diagram for our 32 sources with a DENIS counterpart. Src 10 and Src 28 are situated close to the boundaries of extragalactic sources, but they have been clearly identified with stars in the optical images (in fact, Src 10 is V615 Ori). Only Src 18 and Src 35 may be absorbed quasars, according to the direction of the ...
Context 2
... fitting was performed for the 11 sources in our sample with at least 500 counts (combining PN and MOS detectors). The results are shown in Table 3. The position in the colour-colour diagram of Fig. 5 of the 11 spectroscopically sources studied in this work indicates they are indeed stars. According to that diagram, only Src 18 and Src 35 may be (absorbed) extragalactic sources. General X-ray parameters obtained for these 11 stars are very similar to those observed in stars of the same class in other star-forming regions (e.g. ...
Context 3
... are three types of sources with very low values of log L X /L bol in our sample: (1) stars showing large infrared excess, for which the SED fitting tool gives very high luminosities, (2) intermediate-mass pre-main-sequence or main-sequence stars (A and F spectral types) and (3) Src 18 that may be an AGN instead of a star (see Section 3.2 and Fig. 5). The SED fitting procedure derives bolometric luminosities and temperatures directly and then determine masses using evolutionary tracks (see Robitaille 2008). For stars with large infrared excesses, to obtain a robust value for their luminosity may be difficult since it depends on the accurate determination of the disc (and envelope ...
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... At the distance of Orion, the observed brightness is equivalent to L X ∼ 10 30 erg s −1 . López-García et al. (2013), using XMM-Newton, also found Source 2864 to be X-ray bright, with an uncorrected X-ray brightness similar to their other NGC 2023 targets. ...
Short-duration flares at millimeter wavelengths provide unique insights into the strongest magnetic reconnection events in stellar coronae and combine with longer-term variability to introduce complications to next-generation cosmology surveys. We analyze 5.5 yr of JCMT Transient Survey 850 μ m submillimeter monitoring observations toward eight Gould Belt star-forming regions to search for evidence of transient events or long-duration variability from faint sources. The eight regions (30′ diameter fields), including ∼1200 infrared-selected YSOs, have been observed on average 47 times with integrations of approximately half an hour, or one day total, spread over 5.5 yr. Within this large data set, only two robust faint source detections are recovered: JW 566 in OMC 2/3 and MGM12 2864 in NGC 2023. JW 566, a Class II T Tauri binary system previously identified as an extraordinary submillimeter flare, remains unique, the only clear single-epoch transient detection in this sample with a flare eight times bright than our ∼4.5 σ detection threshold of 55 mJy beam ⁻¹ . The lack of additional recovered flares intermediate between JW 566 and our detection limit is puzzling if smaller events are more common than larger events. In contrast, the other submillimeter variable identified in our analysis, Source 2864, is highly variable on all observed timescales. Although Source 2864 is occasionally classified as a YSO, the source is most likely a blazar. The degree of variability across the electromagnetic spectrum may be used to aid source classification.
... At the distance of Orion, the observed brightness is equivalent to L X ∼ 10 30 erg/s. López-García et al. (2013), using XMM-Newton, also found Source 2864 to be X-ray bright, with an uncorrected x-ray brightness similar to their other NGC 2023 targets. ...
Short-duration flares at millimeter wavelengths provide unique insights into the strongest magnetic reconnection events in stellar coronae, and combine with longer-term variability to introduce complications to next-generation cosmology surveys. We analyze 5.5 years of JCMT Transient Survey 850 micron submillimeter monitoring observations toward eight Gould Belt star-forming regions to search for evidence of transient events or long-duration variability from faint sources. The eight regions (30 arcmin diameter fields), including ~1200 infrared-selected YSOs, have been observed on average 47 times with integrations of approximately half an hour, or one day total spread over 5.5 years. Within this large data set, only two robust faint source detections are recovered: JW 566 in OMC 2/3 and MGM12 2864 in NGC 2023. JW 566, a Class II TTauri binary system previously identified as an extraordinary submillimeter flare, remains unique, the only clear single-epoch transient detection in this sample with a flare eight times bright than our ~4.5 sigma detection threshold of 55 mJy/beam. The lack of additional recovered flares intermediate between JW 566 and our detection limit is puzzling, if smaller events are more common than larger events. In contrast, the other submillimeter variable identified in our analysis, Source 2864, is highly variable on all observed timescales. Although Source 2864 is occasionally classified as a YSO, the source is most likely a blazar. The degree of variability across the electromagnetic spectrum may be used to aid source classification.
Context. Young early-type HAeBe stars are still embedded in the molecular clouds in which they formed. They illuminate reflection nebulae, which shape the surrounding molecular cloud and may trigger star formation. They are therefore ideal places to search for ongoing star formation activity.
Aims. NGC 2023 is illuminated by the Herbig Be star HD 37903. It is the most massive member of a small young cluster with about 30 PMS stars, several of which are Class I objects that still heavily accrete. It might therefore be expected that they might drive molecular outflows. We examined the whole region for outflows.
Methods. We analyzed previously published APEX data to search for and characterize the outflows in the NGC 2023 region. This is the first systematic search for molecular outflows in this region. Since the outflows were mapped in several CO transitions, we can determine their properties quite well.
Results. We have discovered four molecular outflows in the vicinity of NGC 2023, three of which are associated with Class I objects. MIR-63, a bright mid-infrared and submillimeter Class I source, is a binary with a separation of 2″.4 and drives two bipolar outflows orthogonal to each other. The large southeast–northwest outflow excites the Herbig-Haro flow HH 247. MIR-73, a Class I object, which is also a far-infrared source, drives a pole-on outflow. MIR-62 is a Class II object with strong infrared excess and a luminosity of 7 L ⊙ . It is not detected in the far-infrared. The Class I sources have bolometric luminosities of about 20 L ⊙ or lower, that is, they are all low-mass stars. One other far-infrared source, MIR-75, may have powered an outflow in the past because it now illuminates an egg-shaped cavity.
Conclusions. The four outflows are all powered by young stars and are located in the immediate vicinity of NGC 2023. They are at a similar evolutionary stage, which suggests that their formation may have been triggered by the expanding C II region.
The second Gaia Data Release (DR2) contains astrometric and photometric data for more than 1.6 billion objects with mean Gaia G magnitude <20.7, including many Young Stellar Objects (YSOs) in different evolutionary stages. In order to explore the YSO population of the Milky Way, we combined the Gaia DR2 data base with Wide-field Infrared Survey Explorer (WISE) and Planck measurements and made an all-sky probabilistic catalogue of YSOs using machine learning techniques, such as Support Vector Machines, Random Forests, or Neural Networks. Our input catalogue contains 103 million objects from the DR2xAllWISE cross-match table. We classified each object into four main classes: YSOs, extragalactic objects, main-sequence stars, and evolved stars. At a 90 per cent probability threshold, we identified 1 129 295 YSO candidates. To demonstrate the quality and potential of our YSO catalogue, here we present two applications of it. (1) We explore the 3D structure of the Orion A star-forming complex and show that the spatial distribution of the YSOs classified by our procedure is in agreement with recent results from the literature. (2) We use our catalogue to classify published Gaia Science Alerts. As Gaia measures the sources at multiple epochs, it can efficiently discover transient events, including sudden brightness changes of YSOs caused by dynamic processes of their circumstellar disc. However, in many cases the physical nature of the published alert sources are not known. A cross-check with our new catalogue shows that about 30 per cent more of the published Gaia alerts can most likely be attributed to YSO activity. The catalogue can be also useful to identify YSOs among future Gaia alerts.
Owing to a lack of robust principled methods, systematic instrumental uncertainties have generally been ignored in astrophysical data analysis despite wide recognition of the importance of including them. Ignoring calibration uncertainty can cause bias in the estimation of source model parameters and can lead to underestimation of the variance of these estimates. We previously introduced a pragmatic Bayesian method to address this problem. The method is "pragmatic" in that it introduced an ad hoc technique that simplified computation by neglecting the potential information in the data for narrowing the uncertainty for the calibration product. Following that work, we use a principal component analysis to efficiently represent the uncertainty of the effective area of an X-ray (or γ-ray) telescope. Here, however, we leverage this representation to enable a principled, fully Bayesian method that coherently accounts for the calibration uncertainty in high-energy spectral analysis. In this setting, the method is compared with standard analysis techniques and the pragmatic Bayesian method. The advantage of the fully Bayesian method is that it allows the data to provide information not only for estimation of the source parameters but also for the calibration product—here the effective area, conditional on the adopted spectral model. In this way, it can yield more accurate and efficient estimates of the source parameters along with valid estimates of their uncertainty. Provided that the source spectrum can be accurately described by a parameterized model, this method allows rigorous inference about the effective area by quantifying which possible curves are most consistent with the data.
We investigate the plausibility of detecting X-ray emission from a stellar
jet that impacts against a dense molecular cloud. This scenario may be usual
for classical T Tauri stars with jets in dense star-forming complexes. We first
model the impact of a jet against a dense cloud by 2D axisymmetric hydrodynamic
simulations, exploring different configurations of the ambient environment.
Then, we compare our results with XMM-Newton observations of the Herbig-Haro
object HH 248, where extended X-ray emission aligned with the optical knots is
detected at the edge of the nearby IC 434 cloud. Our simulations show that a
jet can produce plasma with temperatures up to 10 MK, consistent with
production of X-ray emission, after impacting a dense cloud. We find that jets
denser than the ambient medium but less dense than the cloud produce detectable
X-ray emission only at the impact onto the cloud. From the exploration of the
model parameter space, we constrain the physical conditions (jet density and
velocity, cloud density) that reproduce well the intrinsic luminosity and
emission measure of the X-ray source possibly associated with HH 248. Thus, we
suggest that the extended X-ray source close to HH 248 corresponds to the jet
impacting on a dense cloud.
Recent studies have confirmed the presence of buckminsterfullerene (C60) in different interstellar and circumstellar environments. However, several aspects regarding C60 in space are not yet well understood, such as the formation and excitation processes, and the connection between C60 and other carbonaceous compounds in the interstellar medium, in particular polycyclic aromatic hydrocarbons (PAHs). In this paper, we study several photodissociation regions (PDRs) where C60 and PAHs are detected and the local physical conditions are reasonably well constrained to provide observational insights into these questions. C60 is found to emit in PDRs where the dust is cool (Td = 20-40 K) and even in PDRs with cool stars. These results exclude the possibility for C60 to be locked in grains at thermal equilibrium in these environments. We observe that PAH and C60 emission are spatially uncorrelated and that C60 is present in PDRs where the physical conditions (in terms of radiation field and hydrogen density) allow for full dehydrogenation of PAHs, with the exception of Ced 201. We also find trends indicative of an increase in C60 abundance within individual PDRs, but these trends are not universal. These results support models where the dehydrogenation of carbonaceous species is the first step toward C60 formation. However, this is not the only parameter involved and C60 formation is likely affected by shocks and PDR age.
Protostellar jets appear at all stages of star formation when the accretion
process is still at work. Jets travel at velocities of hundreds of km/s,
creating strong shocks when interacting with interstellar medium. Several cases
of jets have been detected in X-rays, typically showing soft emission. For the
first time, we report evidence of hard X-ray emission possibly related to
non-thermal processes not explained by previous models of the post-shock
emission predicted in the jet/ambient interaction scenario. HH 80 is located at
the south head of the jet associated to the massive protostar IRAS 18162-2048.
It shows soft and hard X-ray emission in regions that are spatially separated,
with the soft X-ray emission region situated behind the region of hard X-ray
emission. We propose a scenario for HH 80 where soft X-ray emission is
associated to thermal processes from the interaction of the jet with denser
ambient matter and the hard X-ray emission is produced by synchrotron radiation
at the front shock.
