- ID:
- ivo://CDS.VizieR/J/A+A/634/L6
- Title:
- NIR spectrum of interstellar object 2I/Borisov
- Short Name:
- J/A+A/634/L6
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Interstellar objects (ISOs) passing through our Solar System offer a rare opportunity to probe the physical and chemical processes involved in solid body and planet formation in extrasolar systems. The main objective of our study is to search for diagnostic absorption features of water ice in the near-infrared (NIR) spectrum of the second interstellar object 2I/2019 Q4 (Borisov) and compare its ice features to those of the Solar System icy objects. We observed 2I in the NIR on three separate occasions. The first observation was made on 2019 September 19 UT using the SpeX spectrograph at the 3m IRTF and again on September 24 UT with the GNIRS spectrograph at the 8m GEMINI telescope; the last observation was made on October 09 UT with IRTF. The spectra obtained from all three nights appear featureless. No absorption features associated with water ice are detected. Spectral modeling suggests that water grains, if present, comprise no more than 10% of the coma cross section. The comet consistently exhibits a red D-type like spectrum with a spectral slope of about 6% per 1000~\AA, which is similar to that of 1I/'Oumuamua and is comparable to Solar System comets.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/547/A17
- Title:
- NIR spectrum of NGC1705-1
- Short Name:
- J/A+A/547/A17
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study the near-infrared properties of the super star cluster NGC1750-1 to constrain its spatial extent, its stellar population, and its age.
- ID:
- ivo://CDS.VizieR/J/AJ/156/178
- Title:
- NIR transmission spectra of TRAPPIST-1 planets
- Short Name:
- J/AJ/156/178
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The seven approximately Earth-sized transiting planets in the TRAPPIST-1 system provide a unique opportunity to explore habitable- and nonhabitable-zone small planets within the same system. Its habitable-zone exoplanets - due to their favorable transit depths - are also worlds for which atmospheric transmission spectroscopy is within reach with the Hubble Space Telescope (HST) and James Webb Space Telescope (JWST). We present here an independent reduction and analysis of two HST Wide Field Camera 3 (WFC3) near-infrared transit spectroscopy data sets for six planets (b through g). Utilizing our physically motivated detector charge-trap correction and a custom cosmic-ray correction routine, we confirm the general shape of the transmission spectra presented by de Wit et al. (2016Natur.537...69D). Our data reduction approach leads to a 25% increase in the usable data and reduces the risk of confusing astrophysical brightness variations (e.g., flares) with instrumental systematics. No prominent absorption features are detected in any individual planet's transmission spectra; by contrast, the combined spectrum of the planets shows a suggestive decrease around 1.4 {mu}m similar to an inverted water absorption feature. Including transit depths from K2, the SPECULOOS-South Observatory, and Spitzer, we find that the complete transmission spectrum is fully consistent with stellar contamination owing to the transit light source effect. These spectra demonstrate how stellar contamination can overwhelm planetary absorption features in low-resolution exoplanet transit spectra obtained by HST and JWST and also highlight the challenges in combining multi-epoch observations for planets around rapidly rotating spotted 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/541/A143
- Title:
- NLTE Corrections of the Ca lines
- Short Name:
- J/A+A/541/A143
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Extremely metal-poor stars contain the fossil records of the chemical composition of the early Galaxy and it is important to compare Ca abundance with abundances of other light elements, that are supposed to be synthesized in the same stellar evolution phases. The NLTE profiles of the calcium lines were computed with a modified version of the program MULTI, which allows a very good description of the radiation field.
- ID:
- ivo://CDS.VizieR/J/A+A/560/A106
- Title:
- NLTE spectral analysis of white dwarf G191-B2B
- Short Name:
- J/A+A/560/A106
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Hydrogen-rich, DA-type white dwarfs are particularly suited as primary standard stars for flux calibration. State-of-the-art NLTE models consider opacities of species up to trans-iron elements and provide reliable synthetic stellar-atmosphere spectra to compare with observation. We will establish a database of theoretical spectra of stellar flux standards that are easily accessible via a web interface.
1797. 540-690nm Solar Atlas
- ID:
- ivo://CDS.VizieR/J/A+A/525/A74
- Title:
- 540-690nm Solar Atlas
- Short Name:
- J/A+A/525/A74
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Astronomical research dealing with accurate radial velocity measurements need reliable astronomical standards to calibrate the spectrographs and to assess possible systematics. Stellar radial velocity standards offer a reference at the level of a few hundred m/s and are not adequate for most present needs. We aim to show that sunlight reflected by asteroids is a fairly accessible way to record a high-resolution solar spectrum from the whole disk, which can therefore be used as a radial velocity standard and can improve the uncertainties of solar line positions.
- ID:
- ivo://CDS.VizieR/J/other/ApSS/353.347
- Title:
- 398-710nm Sun spectral atlases
- Short Name:
- J/other/ApSS/353
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this work, we present digital and graphical atlases of spectra of both the solar disk-center and of the limb near the Solar poles using data taken at the UTS-IAP & RIAAM (the University of Tabriz Siderostat, telescope and spectrograph jointly developed with the Institut d'Astrophysique de Paris and Research Institute for Astronomy and Astrophysics of Maragha). High resolution and high signal-to-noise ratio (SNR) CCD-slit spectra of the sun for 2 different parts of the disk, namely for {mu}=1.0 (solar center) & for {mu}=0.3 (solar limb) are provided and discussed. While there are several spectral atlases of the solar disk-center, this is the first spectral atlas ever produced for the solar limb at this spectral range. The resolution of the spectra is about R~70000 ({Delta}{lambda}~0.09{AA})} with the signal-to-noise ratio (SNR) of 400-600. The full atlas covers the 3980 to 7100{AA} spectral regions and contains 44 pages with three partial spectra of the solar spectrum put on each page to make it compact. The difference spectrum of the normalized each page to make it compact. The difference spectrum of the normalized solar disk-center and the solar limb is also included in the graphic presentation of the atlas to show the difference of line profiles, including far wings. The identification of most of the significant solar lines are included in the graphic presentation of the atlas. Telluric lines are producing a definite signature on the difference spectra which is easy to notice.
- ID:
- ivo://CDS.VizieR/J/A+A/589/A28
- Title:
- N66, N88 & N25+N26 emission line maps
- Short Name:
- J/A+A/589/A28
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This paper presents [CII], [CI] and CO emission line maps of the star-forming regions N66, N25+N26, and N88 in the metal-poor Local Group dwarf galaxy SMC. The spatial and velocity structure of the large HII region N66 reveals an expanding ring of shocked molecular gas centered on the exciting star cluster NGC346, whereas a more distant dense molecular cloud is being eroded by UV radiation from the same cluster. In the N25+N26 and N88 maps, diffuse [CII] emission at a relatively low surface brightness extends well beyond the compact boundaries of the bright emission associated with the HII regions. In all regions, the distribution of this bright [CII] emission and the less prominent [CI] emission closely follows the outline of the CO complexes, but the intensity of the [CII] and [CI] emission is generally anticorrelated, which can be understood by the action of photodissociation and photoionization processes. Notwithstanding the overall similarity of CO and [CII] maps, the intensity ratio of these lines varies significantly, mostly due to changes in CO brightness. [CII] emission line profiles are up to 50% wider in velocity than corresponding CO profiles. A radiative transfer analysis shows that the [CII] line is the dominant tracer of (CO-dark) molecular hydrogen in the SMC. CO emission traces only a minor fraction of the total amount of gas. The similarity of the spatial distribution and line profile shape, and the dominance of molecular gas associated with CII rather than CO emission imply that in the low-metallicity environment of the SMC the small amount of dense molecular gas traced by CO is embedded in the much more extended molecular gas traced only by [CII] emission. The contribution from neutral atomic and ionized hydrogen zones is negligible in the star-forming regions observed
1800. 14N/15N ratio in YSOs
- 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.
