- ID:
- ivo://CDS.VizieR/J/A+A/647/A109
- Title:
- NIR observations of LDN1512
- Short Name:
- J/A+A/647/A109
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Light scattering at near-infrared wavelengths has been used to study the optical properties of the interstellar dust grains, but these studies are limited by the assumptions on the strength of the radiation field. On the other hand, thermal dust emission can be used to constrain the properties of the radiation field, although this is hampered by uncertainty about the dust emissivity. Combining light scattering and emission studies allows us to probe the properties of the dust grains in detail. We wish to study if current dust models allow us to model a molecular cloud simultaneously in the near infrared (NIR) and far infrared (FIR) wavelengths and compare the results with observations. Our aim is to place constraints on the properties of the dust grains and the strength of the radiation field. We present computations of dust emission and scattered light of a quiescent molecular cloud LDN1512. We use NIR observations covering the J, H, and Ks bands, and FIR observations between 250 and 500 micron from Herschel space telescope. We construct radiative transfer models for LDN1512 that include an anisotropic radiation field and a three-dimensional cloud model. We are able to reproduce the observed FIR observations, with a radiation field derived from the DIRBE observations, with all of the tested dust models. However, with the same density distribution and the assumed radiation field, the models fail to reproduce the observed NIR scattering in all cases except for models that take into account dust evolution via coagulation and mantle formation. The intensity from the diffuse interstellar medium (ISM) like, dust models can be increased to match the observed one by reducing the derived density, increasing the intensity of the background sky and the strength of the radiation field between factors from 2 to 3. We find that the column densities derived from our radiative transfer modelling can differ by a factor of up to two, compared to the column densities derived from the observations with modified blackbody fits. The discrepancy in the column densities is likely caused because of temperature difference between a modified blackbody fit and the real spectra.The difference between the fitted temperature and the true temperature could be as high as {Delta}T=+/-1.5K. We show that the observed dust emission can be reproduced with several different assumptions about the properties of the dust grains. However, in order to reproduce the observed scattered surface brightness dust evolution must be taken into account.
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- ID:
- ivo://CDS.VizieR/J/ApJ/741/35
- Title:
- NIR photometry and polarization in NGC 2264
- Short Name:
- J/ApJ/741/35
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Near-infrared imaging polarimetry in the J, H, and Ks bands has been carried out for the protostellar cluster region around NGC 2264 IRS 2 in the Monoceros OB1 molecular cloud. Various infrared reflection nebula clusters (IRNCs) associated with NGC 2264 IRS 2 and the IRAS 12 S1 core, as well as local infrared reflection nebulae (IRNe), were detected. The illuminating sources of the IRNe were identified with known or new near- and mid-infrared sources. In addition, 314 point-like sources were detected in all three bands and their aperture polarimetry was studied. Using a color-color diagram, reddened field stars and diskless pre-main-sequence stars were selected to trace the magnetic field (MF) structure of the molecular cloud. The mean polarization position angle of the point-like sources is 81+/-29{deg} in the cluster core, and 58+/-24{deg} in the perimeter of the cluster core, which is interpreted as the projected direction on the sky of the MF in the observed region of the cloud. The Chandrasekhar-Fermi method gives a rough estimate of the MF strength to be about 100uG. A comparison with recent numerical simulations of the cluster formation implies that the cloud dynamics is controlled by the relatively strong MF. The local MF direction is well associated with that of CO outflow for IRAS 12 S1 and consistent with that inferred from submillimeter polarimetry. In contrast, the local MF direction runs roughly perpendicular to the Galactic MF direction.
- ID:
- ivo://CDS.VizieR/J/ApJS/211/3
- Title:
- NIR photometry variability in {rho} Oph
- Short Name:
- J/ApJS/211/3
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Presented are the results of a near-IR photometric survey of 1678 stars in the direction of the {rho} Ophiuchus ({rho} Oph) star forming region using data from the 2MASS Calibration Database. For each target in this sample, up to 1584 individual J-, H-, and Ks-band photometric measurements with a cadence of ~1 day are obtained over three observing seasons spanning ~2.5 yr; it is the most intensive survey of stars in this region to date. This survey identifies 101 variable stars with {Delta}Ks-band amplitudes from 0.044 to 2.31 mag and {Delta}(J-Ks) color amplitudes ranging from 0.053 to 1.47 mag. Of the 72 young {rho} Oph star cluster members included in this survey, 79% are variable; in addition, 22 variable stars are identified as candidate members. Based on the temporal behavior of the Ks time-series, the variability is distinguished as either periodic, long time-scale or irregular. This temporal behavior coupled with the behavior of stellar colors is used to assign a dominant variability mechanism. A new period-searching algorithm finds periodic signals in 32 variable stars with periods between 0.49 to 92 days. The chief mechanism driving the periodic variability for 18 stars is rotational modulation of cool starspots while 3 periodically vary due to accretion-induced hot spots. The time-series for six variable stars contains discrete periodic "eclipse-like" features with periods ranging from 3 to 8 days. These features may be asymmetries in the circumstellar disk, potentially sustained or driven by a proto-planet at or near the co-rotation radius. Aperiodic, long time-scale variations in stellar flux are identified in the time-series for 31 variable stars with time-scales ranging from 64 to 790 days. The chief mechanism driving long time-scale variability is variable extinction or mass accretion rates. The majority of the variable stars (40) exhibit sporadic, aperiodic variability over no discernable time-scale. No chief variability mechanism could be identified for these variable stars.
- ID:
- ivo://CDS.VizieR/J/A+A/617/A7
- Title:
- Nitrogen isotopic ratio in prestellar cores
- Short Name:
- J/A+A/617/A7
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The ^15^N fractionation has been observed to show large variations among astrophysical sources, depending both on the type of target and on the molecular tracer used. These variations cannot be reproduced by the current chemical models. Until now, the ^14^N/^15^N ratio in N_2_H^+^ has been accurately measured in only one prestellar source, L1544, where strong levels of fractionation, with depletion in ^15^N, are found (^14^N/^15^N~1000). In this paper we extend the sample to three more bona fide prestellar cores, in order to understand if the antifractionation in N_2_H^+^ is a common feature of this kind of sources. Methods. We observed N_2_H^+^ , N^15^NH^+^ and ^15^NNH^+^ in L183, L429 and L694-2 with the IRAM 30m telescope. We modeled the emission with a non-local radiative transfer code in order to obtain accurate estimates of the molecular column densities, including the one for the optically thick N_2_H^+^ . We used the most recent collisional rate coefficients available, and with these we also re-analysed the L1544 spectra previously published. The obtained isotopic ratios are in the range 630-770 and significantly differ with the value, predicted by the most recent chemical models, of ~440, close to the protosolar value. Our prestellar core sample shows high level of depletion of ^15^N in diazenylium, as previously found in L1544. A revision of the N chemical networks is needed in order to explain these results.
- ID:
- ivo://CDS.VizieR/J/A+A/555/A109
- Title:
- ^14^N/^15^N isotopic ratio in L1544
- Short Name:
- J/A+A/555/A109
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Samples of pristine solar system material found in meteorites and interplanetary dust particles are highly enriched in ^15^N. Conspicuous nitrogen isotopic anomalies have also been measured in comets, and the ^14^N/^15^N abundance ratio of the Earth is itself higher than the recognised presolar value by almost a factor of two. Ion/molecules, low-temperature chemical reactions in the proto-solar nebula have been repeatedly indicated as being responsible for these ^15^N-enhancements. We have searched for ^15^N variants of the N2H^+^ ion in L1544, a prototypical starless cloud core that is one of the best candidate sources for detection owing to its low central core temperature and high CO depletion. The goal is to evaluate accurate and reliable ^14^N/^15^N ratio values for this species in the interstellar gas. A deep integration of the ^15^NNH^+^(1-0) line at 90.4GHz was obtained with the IRAM 30m telescope. Non-LTE radiative transfer modelling was performed on the J=1-0 emissions of the parent and ^15^N-containing dyazenilium ions, using a Bonnor-Ebert sphere as a model for the source. A high-quality fit of the N2H^+^(1-0) hyperfine spectrum has allowed us to derive a revised value of the N2H+ column density in L1544. Analysis of the observed N^15^NH^+^ and ^15^NNH^+^ spectra yielded an abundance ratio N(N^15^NH^+^)/N(^15^NNH^+^)=1.1+/-0.3. The obtained ^14^N/^15^N isotopic ratio is ~1000+/-200, suggestive of a sizeable ^15^N depletion in this molecular ion. Such a result is not consistent with the prediction of the current nitrogen chemical models. Since chemical models predict high ^15^N fractionation of N_2_H^+^, we suggest that ^15^N^14^N, or ^15^N in some other molecular form, is preferentially depleted onto dust grains.
- ID:
- ivo://CDS.VizieR/J/A+A/644/A29
- Title:
- 14N/15N ratio in YSOs
- Short Name:
- J/A+A/644/A29
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The nitrogen isotopic ratio is considered an important diagnostic tool of the star formation process, and N_2_H^+^ is particularly important because it is directly linked to molecular nitrogen N_2_. However, theoretical models still lack to provide an exhaustive explanation for the observed^14^N/^15^N values. Recent theoretical works suggest that the^14^N/^15^N behaviour is dominated by two competing reactions that destroy N_2_H^+^: dissociative recombination and reaction with CO. When CO is depleted from the gas phase, if N_2_H^+^ recombination rate is lower with respect to the N^15^NH^+^ one, the rarer isotopologue is destroyed faster. In prestellar cores, due to a combination of low temperatures and high densities, most CO is frozen in ices onto the dust grains, leading to high levels of depletion. On the contrary, in protostellar cores, where temperature are higher, CO ices evaporate back to the gas phase. This implies that the N_2_H^+^ isotopic ratio in protostellar cores should be lower than the one in prestellar cores, and consistent with the elemental value of ~440. We aim to test this hypothesis, producing the first sample of N_2_H^+^ /N^15^NH^+^ measurements in low mass protostars. We observe the N_2_H^+^ and N^15^NH^+^ lowest rotational transition towards six young stellar objects in Perseus and Taurusmolecular clouds. We model the spectra with a custom python code using a constant T_ex_ approach to fit the observations. We discuss in appendix the validity of this hypothesis. The derived column densities are used to compute the nitrogen isotopic ratios. Our analysis yields an average of^14^N/^15^N|_pro_=420+/-15 in the protostellar sample. This is consistent with the protosolar value of 440, and significantly lower than the average value previously obtained in a sample of prestellar objects. Our results are in agreement with the hypothesis that, when CO is depleted from the gas-phase, dissociative recombinations with free electrons destroy N^15^NH^+^ faster than N_2_H^+^ , leading to high isotopic ratios in prestellar cores, where carbon monoxide is frozen onto dust grains.
- ID:
- ivo://CDS.VizieR/J/ApJ/707/103
- Title:
- Observation of Ser FIRS 1 at 230GHz
- Short Name:
- J/ApJ/707/103
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the first results of a program to characterize the disk and envelope structure of typical Class 0 protostars in nearby low-mass star-forming regions. We use Spitzer Infrared Spectrograph (IRS) mid-infrared spectra, high-resolution Combined Array for Research in Millimeter-wave Astronomy (CARMA) 230GHz continuum imaging, and two-dimensional radiative transfer models to constrain the envelope structure, as well as the size and mass of the circumprotostellar disk in Serpens FIRS 1. The primary envelope parameters (centrifugal radius, outer radius, outflow opening angle, and inclination) are well constrained by the spectral energy distribution (SED), including Spitzer IRAC and MIPS photometry, IRS spectra, and 1.1mm Bolocam photometry. These together with the excellent uv-coverage (4.5-500k{lambda}) of multiple antenna configurations with CARMA allow for a robust separation of the envelope and a resolved disk. The SED of Serpens FIRS 1 is best fit by an envelope with the density profile of a rotating, collapsing spheroid with an inner (centrifugal) radius of approximately 600AU, and the millimeter data by a large resolved disk with M_disk_~1.0M_{sun}_ and R_disk_~300AU.
- ID:
- ivo://CDS.VizieR/J/A+A/440/151
- Title:
- Observations at 850um in Perseus clusters
- Short Name:
- J/A+A/440/151
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a complete survey of current star formation in the Perseus molecular cloud, made at 850 and 450{mu} with SCUBA at the JCMT. Covering 3deg^2^, this submillimetre continuum survey for protostellar activity is second in size only to that of rho Ophiuchus (Johnstone et al., 2004ApJ...611L..45J). Complete above 0.4M_{sun}_ (5{sigma} detection in a 14" beam), we detect a total of 91 protostars and pre-stellar cores. Of these, 80% lie in clusters, representative of star formation across the Galaxy. Two of the groups of cores are associated with the young stellar clusters IC 348 and NGC 1333, and are consistent with a steady or reduced star formation rate in the last 0.5Myr, but not an increasing one. In Perseus, 40-60% of cores are in small clusters (<50M_{sun}_) and isolated objects, much more than the 10% suggested from infrared studies. Complementing the dust continuum, we present a C^18^O map of the whole cloud at 1' resolution.
- ID:
- ivo://CDS.VizieR/J/A+A/606/A82
- Title:
- Observed chemical structure of L1544
- Short Name:
- J/A+A/606/A82
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the emission maps of 39 different molecular transitions belonging to 22 different molecules in the central 6.25 arcmin^2^ of L1544. We classified our sample in five families, depending on the location of their emission peaks within the core. Furthermore, to systematically study the correlations among different molecules, we have performed the principal component analysis (PCA) on the integrated emission maps. The PCA allows us to reduce the amount of variables in our dataset. Finally, we compare the maps of the first three principal components with the H_2_ column density map, and the T_dust_ map of the core. The results of our qualitative analysis is the classification of the molecules in our dataset in the following groups: (i) the c-C_3_H_2_ family (carbon chain molecules like C_3_H and CCS), (ii) the dust peak family (nitrogen-bearing species like N_2_H^+^ ), (iii) the methanol peak family (oxygen-bearing molecules like methanol, SO and SO_2_, (iv) the HNCO peak family (HNCO, propyne and its deuterated isotopologues). Only HC^18^O^+^ and ^13^CS do not belong to any of the above mentioned groups. The principal component maps allow us to confirm the (anti-)correlations among different families that were described in a first qualitative analysis, but also points out the correlation that could not be inferred before. For example, the molecules belonging to the dust peak and the HNCO peak families correlate in the third principal component map, hinting on a chemical/physical correlation.
- ID:
- ivo://CDS.VizieR/J/A+A/615/A40
- Title:
- OB stars in N206 in the LMC
- Short Name:
- J/A+A/615/A40
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Context. Clusters or associations of early-type stars are often associated with a "superbubble" of hot gas. The formation of such superbubbles is caused by the feedback from massive stars. The complex N 206 in the Large Magellanic Cloud (LMC) exhibits a superbubble and a rich massive star population. Aims. Our goal is to perform quantitative spectral analyses of all massive stars associated with the N 206 superbubble in order to determine their stellar and wind parameters. We compare the superbubble energy budget to the stellar energy input and discuss the star formation history of the region. Methods. We observed the massive stars in the N 206 complex using the multi-object spectrograph FLAMES at ESO's Very Large Telescope (VLT). Available ultra-violet (UV) spectra from archives are also used. The spectral analysis is performed with Potsdam Wolf-Rayet (PoWR) model atmospheres by reproducing the observations with the synthetic spectra. Results. We present the stellar and wind parameters of the OB stars and the two Wolf-Rayet (WR) binaries in the N 206 complex. Twelve percent of the sample show Oe/Be type emission lines, although most of them appear to rotate far below critical. We found eight runaway stars based on their radial velocity. The wind-momentum luminosity relation of our OB sample is consistent with the expectations. The Hertzsprung-Russell diagram (HRD) of the OB stars reveals a large age spread (1-30Myr), suggesting different episodes of star formation in the complex. The youngest stars are concentrated in the inner part of the complex, while the older OB stars are scattered over outer regions. We derived the present day mass function for the entire N 206 complex as well as for the cluster NGC 2018. The total ionizing photon flux produced by all massive stars in the N 206 complex is Q_0_~=5x10^50^s^-1^, and the mechanical luminosity of their stellar winds amounts to L_mec_=1.7x10^38^erg/s. Three very massive Of stars are found to dominate the feedback among 164 OB stars in the sample. The two WR winds alone release about as much mechanical luminosity as the whole OB star sample. The cumulative mechanical feedback from all massive stellar winds is comparable to the combined mechanical energy of the supernova explosions that likely occurred in the complex. Accounting also for the WR wind and supernovae, the mechanical input over the last five Myr is ~=2.3x10^52^erg. Conclusions. The N206 complex in the LMC has undergone star formation episodes since more than 30Myr ago. From the spectral analyses of its massive star population, we derive a current star formation rate of 2.2x10^-3^M_{sun}_/yr. From the combined input of mechanical energy from all stellar winds, only a minor fraction is emitted in the form of X-rays. The corresponding input accumulated over a long time also exceeds the current energy content of the complex by more than a factor of five. The morphology of the complex suggests a leakage of hot gas from the superbubble.
