Towards a better classification of unclear eruptive variables: the cases of V2492 Cyg, V350 Cep, and ASASSN-15qi

Eruptive variables are young stars that show episodic variations of brightness: EXors/FUors variations are commonly associated with enhanced accretion outbursts occurring at intermittent cadence of months/years (EXors) and decades/centuries (FUors). Variations that can be ascribed to a variable extinction along their line of sight are instead classified as UXors. We aim at investigating the long-term photometric behaviour of three sources classified as eruptive variables. We present data from the archival plates of the Asiago Observatory relative to the fields where the targets are located. For the sake of completeness we have also analysed the Harvard plates of the same regions that cover a much longer historical period, albeit at a lower sensitivity, however we are only able to provide upper limits. A total of 273 Asiago plates were investigated, providing a total of more than 200 magnitudes for the three stars, which cover a period of about 34 yr between 1958 and 1991. We have compared our data with more recently collected literature data. Our plates analysis of V2492 Cyg provides historical upper limits that seem not to be compatible with the level of the activity monitored during the last decade. Therefore, recently observed accretion phenomena could be associated with the outbursting episodes, more than repetitive obscuration. While a pure extinction does not seem the only mechanism responsible for the ASASSN-15qi fluctuations, it can account quite reasonably for the recent V350 Cep variations.Comment: 12 pages, accepted by A&

The 2016-2017 peak luminosity of the pre-main sequence variable V2492 Cyg

V2492 Cyg is a young pre-main sequence star presenting repetitive brightness variations of significant amplitude (Delta R > 5 mag) whose physical origin has been ascribed to both extinction (UXor-type) and accretion (EXor-type) variability, although their mutual proportion has not been clarified yet. Recently, V2492 Cyg has reached a level of brightness ever registered in the period of its documented activity. Optical and near-infrared photometry and spectroscopy have been obtained in October 2016 and between March and July 2017. The source has remained bright until the end of May 2017, then it started to rapidly fade since the beginning of June at a rate of about 0.08 mag/day. On mid-July 2017 the source has reached the same low-brightness level as two years before. Extinction and mass accretion rate were derived by means of the luminosity of the brightest lines, in particular Halpha and Hbeta. A couple of optical high-resolution spectra are also presented to derive information on the gas kinematics. Visual extinction variations do not exceed a few magnitudes, while the mass accretion rate is estimated to vary from less than 10^-8 up to a few 10^-7 M_sun/yr. This latter is comparable to that estimated on the previous high-state in 2010, likely occurred under more severe extinction conditions. The combined analysis of the optical and near-infrared (NIR) observations extends to the present event the original suggestion that the V2492 Cyg variability is a combination of changing extinction and accretion.Comment: Accepted by A&

Exchange Currents in Photoproduction of Baryon Resonances

We calculate photoexcitation amplitudes for several nucleon and delta resonances. We use a chiral quark model including two-body exchange currents. The two-body currents give important contributions. For the delta (1232) and the D13 (1520) we observe that the individual exchange current contributions considerably cancel each other while in the case of the Roper resonance and the S11 (1535) we get a reinforcement of the two-body amplitudes. In comparison with present experimental data, we obtain both for the S11 (1535) and for the Roper resonance an improvement with respect to the impulse approximation.Comment: 9 pages, 1 figur

Water distribution in shocked regions of the NGC1333-IRAS4A protostellar outflow

We present the study of the H2O spatial distribution at two bright shocked regions along IRAS4A, one of the strongest H2O emitters among the Class 0 outflows. We obtained Herschel-PACS maps of the IRAS4A outflow and HIFI observations of two shocked positions. The largest HIFI beam of 38 arcsec at 557 GHz was mapped in several key water lines with different upper energy levels, to reveal possible spatial variations of the line profiles. We detect four H2O lines and CO (16-15) at the two selected positions. In addition, transitions from related outflow and envelope tracers are detected. Different gas components associated with the shock are identified in the H2O emission. In particular, at the head of the red lobe of the outflow, two distinct gas components with different excitation conditions are distinguished in the HIFI emission maps: a compact component, detected in the ground-state water lines, and a more extended one. Assuming that these two components correspond to two different temperature components observed in previous H2O and CO studies, the excitation analysis of the H2O emission suggests that the compact (about 3 arcsec) component is associated with a hot (T~1000 K) gas with densities ~(1-4)x10^5 cm^{-3}, whereas the extended one (10-17 arcsec) traces a warm (T~300-500 K) and dense gas (~(3-5)x10^7 cm^{-3}). Finally, using the CO (16-15) emission observed at R2, we estimate the H2O/H2 abundance of the warm and hot components to be (7-10)x10^{-7} and (3-7)x10^{-5}. Our data allowed us, for the first time, to resolve spatially the two temperature components previously observed with HIFI and PACS. We propose that the compact hot component may be associated with the jet that impacts the surrounding material, whereas the warm, dense, and extended component originates from the compression of the ambient gas by the propagating flow.Comment: 13 pages, 11 figures. Accepted for publication in Astronomy and Astrophysic

[12CII] and [13CII] 158 mum emission from NGC 2024: Large column densities of ionized carbon

Context: We analyze the NGC 2024 HII region and molecular cloud interface using [12CII] and [13CII] observations. Aims: We attempt to gain insight into the physical structure of the interface layer between the molecular cloud and the HII region. Methods. Observations of [12CII] and [13CII] emission at 158 {\mu}m with high spatial and spectral resolution allow us to study the detailed structure of the ionization front and estimate the column densities and temperatures of the ionized carbon layer in the PDR. Results: The [12CII] emission closely follows the distribution of the 8 mum continuum. Across most of the source, the spectral lines have two velocity peaks similar to lines of rare CO isotopes. The [13CII] emission is detected near the edge-on ionization front. It has only a single velocity component, which implies that the [12CII] line shape is caused by self-absorption. An anomalous hyperfine line-intensity ratio observed in [13CII] cannot yet be explained. Conclusions: Our analysis of the two isotopes results in a total column density of N(H)~1.6\times10^23 cm^-2 in the gas emitting the [CII] line. A large fraction of this gas has to be at a temperature of several hundred K. The self-absorption is caused by a cooler (T<=100 K) foreground component containing a column density of N(H)~10^22 cm^-2

The cooling of atomic and molecular gas in DR21

We present an overview of a high-mass star formation region through the major (sub-)mm, and far-infrared cooling lines to gain insight into the physical conditions and the energy budget of the molecular cloud. We used the KOSMA 3m telescope to map the core ($10'\times 14'$) of the Galactic star forming region DR 21/DR 21 (OH) in the Cygnus X region in the two fine structure lines of atomic carbon CI and four mid-$J$ transitions of CO and $^{13}$CO, and CS J=7\TO6. These observations have been combined with FCRAO J=1\TO0 observations of $^{13}$CO and C$^{18}$O. Five positions, including DR21, DR21 (OH), and DR21 FIR1, were observed with the ISO/LWS grating spectrometer in the \OI 63 and 145 $\mu$m lines, the \CII 158 $\mu$m line, and four high-$J$ CO lines. We discuss the intensities and line ratios at these positions and apply Local Thermal Equilibrium (LTE) and non-LTE analysis methods in order to derive physical parameters such as masses, densities and temperatures. The CO line emission has been modeled up to J=20. From non-LTE modeling of the low- to high-$J$ CO lines we identify two gas components, a cold one at temperatures of T_\RM{kin}\sim 30-40 K, and one with T_\RM{kin}\sim 80-150 K at a local clump density of about n(H$_2$)$\sim 10^4-10^6$ cm$^{-3}$. While the cold quiescent component is massive containing typically more than 94 % of the mass, the warm, dense, and turbulent gas is dominated by mid- and high-$J$ CO line emission and its large line widths. The medium must be clumpy with a volume-filling of a few percent. The CO lines are found to be important for the cooling of the cold molecular gas, e.g. at DR21 (OH). Near the outflow of the UV-heated source DR21, the gas cooling is dominated by line emission of atomic oxygen and of CO

GIARPS High-resolution Observations of T Tauri stars (GHOsT). I. Jet line emission

The mechanism for jet formation in the disks of T Tauri stars is poorly understood. Observational benchmarks to launching models can be provided by tracing the physical properties of the kinematic components of the wind and jet in the inner 100 au of the disk surface. In the framework of the GHOsT (GIARPS High-resolution Observations of T Tauri stars) project, we aim to perform a multi-line analysis of the velocity components of the gas in the jet acceleration zone. We analyzed the GIARPS-TNG spectra of six objects in the Taurus-Auriga complex (RY Tau, DG Tau, DL Tau, HN Tau, DO Tau, RW Aur A). Thanks to the combined high-spectral resolution (R=50000-115000) and wide spectral coverage (~400-2400 nm) we observed several O, S+, N, N+, and Fe+ forbidden lines spanning a large range of excitation and ionization conditions. In four objects (DG Tau, HN Tau, DO Tau, RW Aur A), temperature (T_e), electron and total density (n_e, n_H), and fractional ionization (x_e) were derived as a function of velocity through an excitation and ionization model. The abundance of gaseous iron, X(Fe), a probe of the dust content in the jet, was derived in selected velocity channels. The physical parameters vary smoothly with velocity, suggesting a common origin for the different kinematic components. In DG Tau and HN Tau, T_e, x_e, and X(Fe) increase with velocity (roughly from 6000 K, 0.05, 10% X(Fe)_sun to 15000 K, 0.6, 90% X(Fe)_sun). This trend is in agreement with disk-wind models in which the jet is launched from regions of the disk at different radii. In DO Tau and RW Aur A, we infer x_e < 0.1, n_H ~10^6-7 cm^-3, and X(Fe) <~ X(Fe)_sun at all velocities. These findings are tentatively explained by the formation of these jets from dense regions inside the inner, gaseous disk, or as a consequence of their high degree of collimation.Comment: Accepted by A&

GIARPS High-resolution Observations of T Tauri stars (GHOsT). III. A pilot study of stellar and accretion properties

The mass-accretion rate, Macc, is a crucial parameter for the study of the evolution of accretion disks around young low-mass stellar objects (YSOs) and for planet formation studies. The Taurus star forming region (SFR) is rich in pre-main sequence (PMS) stars, most of them of the T Tauri class. A variety of methodologies have been used in the past to measure mass accretion in samples of YSOs in Taurus, but despite being a general benchmark for star formation studies, a comprehensive and systematic analysis of the Taurus T Tauri population, where the stellar and accretion properties are derived homogeneously and simultaneously, is still missing. As part of the GIARPS High-resolution Observations of T Tauri stars (GHOsT) project, here we present a pilot study of the stellar and accretion properties of seven YSOs in Taurus using the spectrograph GIARPS at the Telescopio Nazionale Galileo (TNG). Contemporaneous low-resolution spectroscopic and photometric ancillary observations allow us to perform an accurate flux calibration of the high-resolution spectra. The simultaneity of the high-resolution, wide-band spectroscopic observations, from the optical to the near-infrared (NIR), the veiling measurements in such wide spectral range, and many well-calibrated emission line diagnostics allows us to derive the stellar and accretion properties of the seven YSOs in a homogeneous and self-consistent way. The procedures and methodologies presented here will be adopted in future works for the analysis of the complete GHOsT data set. We discuss the accretion properties of the seven YSOs in comparison with the 90\% complete sample of YSOs in the Lupus SFR and investigate possibilities for the origin of the continuum excess emission in the NIR.

A dentigerous cyst associated with bilaterally impacted mandibular canines in a girl: a case report

Introduction: A dentigerous cyst is the most common developmental odontogenic cyst and is frequently noted as an incidental finding on radiographs. The most common teeth affected are impacted mandibular third molars and permanent maxillary canines. This case involves a dentigerous cyst encompassing the right and left impacted mandibular canines and crossing the midline. This is, to the best of our knowledge, the first reported case of a dentigerous cyst encompassing non-adjacent teeth and crossing the midline. Case presentation: The patient presented to our orthodontic clinic for treatment of malocclusion. The patient was a 10-year, one-month-old Caucasian girl with a dentigerous cyst encompassing the right and left impacted mandibular canines and crossing the midline. Conclusion: This case involves an unusual clinical and radiographic presentation of a dentigerous cyst. It shows a new variant of presentation that medical professionals, specifically dentists and radiologists, should be aware of, since a dentigerous cyst crossing the midline has not been previously reported as far as we are aware. This additional knowledge is important for inclusion on differential diagnosis lists and aids in the development of a proper treatment plan