- ID:
- ivo://CDS.VizieR/J/A+A/632/A32
- Title:
- Carbon depletion observed inside T Tauri inner rims
- Short Name:
- J/A+A/632/A32
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The carbon content of protoplanetary disks is an important parameter to characterize planets formed at different disk radii. There is some evidence from far-infrared and submillimeter observations that gas in the outer disk is depleted in carbon, with a corresponding enhancement of carbon-rich ices at the disk midplane. Observations of the carbon content inside of the inner sublimation rim could confirm how much cpc on remains locked in kilometer size bodies in the disk. I aim to determine the density, temperature, and carbon abundance inside the disk dust sublimation rim in a set of T Tauri stars with full protoplanetary disks. Using medium-resolution, near-infrared (0.8 to 2.5um) spectra and the new GAIA DR2 distances, I self-consistently determine the stellar, extinction, veiling, and accretion properties of the 26 stars in my sample. From these values, and non-accreting T Tauri spectral templates, I extract the inner disk excess of the target stars from their observed spectra. Then I identify a series of C0 recombination lines in 18 of these disks and use the CHIANTI atomic line database with an optically thin slab model to constrain the average ne, Te, and nC for these lines in the five disks with a complete set of lines. By comparing these values with other slab models of the inner disk using the Cloudy photoionization code, I also constrain nH and the carbon abundance, XC, and hence the amount of carbon 'missing' from the slab. For one disk, DR Tau, I use relative abundances for the accretion stream from the literature to also determine XSi and XN . The inner disks modeled here are extremely dense (nH~10^16^cm^-3^), warm (Te~4500K), and moderately ionized (logXe~3.3). Three of the five modeled disks show robust carbon depletion up to a factor of 42 relative to the solar value. I discuss multiple ways in which the 'missing' carbon could be locked out of the accreting gas. Given the high-density inner disk gas, evidence for radial drift, and lack of obvious gaps in these three systems, their carbon depletion is most consistent with the 'missing' carbon being sequestered in kilometer size bodies. For DR Tau, nitrogen and silicon are also depleted by factors of 45 and 4, respectively, suggesting that the kilometer size bodies into which the grains are locked were formed beyond the N_2_ snowline. I explore briefly what improvements in the models and observations are needed to better address this topic in the future.
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- ID:
- ivo://CDS.VizieR/J/ApJS/234/31
- Title:
- Carbon stars from LAMOST using machine learning
- Short Name:
- J/ApJS/234/31
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this work, we present a catalog of 2651 carbon stars from the fourth Data Release (DR4) of the Large Sky Area Multi-Object Fiber Spectroscopy Telescope (LAMOST). Using an efficient machine-learning algorithm, we find these stars from more than 7 million spectra. As a by-product, 17 carbon-enhanced metal- poor turnoff star candidates are also reported in this paper, and they are preliminarily identified by their atmospheric parameters. Except for 176 stars that could not be given spectral types, we classify the other 2475 carbon stars into five subtypes: 864 C-H, 226 C-R, 400 C-J, 266 C-N, and 719 barium stars based on a series of spectral features. Furthermore, we divide the C-J stars into three subtypes, C-J(H), C-J(R), and C-J(N), and about 90% of them are cool N-type stars as expected from previous literature. Besides spectroscopic classification, we also match these carbon stars to multiple broadband photometries. Using ultraviolet photometry data, we find that 25 carbon stars have FUV detections and that they are likely to be in binary systems with compact white dwarf companions.
- ID:
- ivo://CDS.VizieR/J/A+A/330/505
- Title:
- Carbon stars IR emission
- Short Name:
- J/A+A/330/505
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Spectroscopic and photometric data relative to a sample of 55 carbon stars showing the 11.3{mu}m feature have been fitted in the wavelength range between 0.4 and 100{mu}m by means of a radiative transfer model using the laboratory extinction spectra of amorphous carbon and silicon carbide (SiC) grains. The transfer code allows to determine in a self-consistent way the grain equilibrium temperature of the various species at different distances from the central star and gives all the relevant circumstellar parameters which can be very important for the evolutionary study of carbon stars. In order to get meaningful information on the nature and physical properties of the dust grains responsible for the 11.3{mu}m feature and the underlying continuum, the fitting procedure of the spectr a has been applied individually to every single source. For this reason it has been possible to take into account any variation in position and shape of the band from source to source. Our analysis show that all the sources, in addition to the amorphous carbon grains accounting for the continuum emission, need always the presence of {alpha}-SiC particles while some of them require also {beta}-SiC. Moreover, the presence of one or both types of SiC particles seems not correlated neither with the total optical thickness nor with any other physical and geometrical parameters of the circumstellar envelope. The best-fit parameters found in this work have been used to calculate the mass-loss rate from the central stars. The clear correlation, that we find between the strength of the SiC feature and the total mass loss-rate, confirms the results already found by other authors for the same kind of sources and derived from the observed CO emission lines.
- ID:
- ivo://CDS.VizieR/J/ApJ/900/42
- Title:
- CARMENES obs. of the binary system LB-1
- Short Name:
- J/ApJ/900/42
- Date:
- 21 Mar 2022 09:26:37
- Publisher:
- CDS
- Description:
- The mass, origin, and evolutionary stage of the binary system LB-1 have been intensely debated, following the claim that it hosts an ~70M_{sun}_ black hole, in stark contrast with the expectations for Galactic remnants. We conducted a high-resolution, phase-resolved spectroscopic study of its Paschen lines, using the Calar Alto 3.5m telescope. We find that Pa{beta} and Pa{gamma} (after subtraction of the stellar absorption component) are well fitted with a standard double-peaked disk profile. We measured the velocity shifts of the red and blue peaks at 28 orbital phases: the line center has an orbital motion in perfect antiphase with the secondary, and the radial velocity amplitude ranges from 8 to 13km/s, for different methods of profile modeling. We interpret this curve as proof that the disk traces the orbital motion of the primary, ruling out the circumbinary disk and the hierarchical triple scenarios. The phase-averaged peak-to-peak half-separation (a proxy for the projected rotational velocity of the outer part of the disk) is ~70km/s, larger than the orbital velocity of the secondary and inconsistent with a circumbinary disk. From those results, we infer a primary mass 4-8 times higher than the secondary mass. Moreover, we show that the intensity ratio of the blue and red peaks has a sinusoidal behavior in phase with the secondary, which we attribute to external irradiation of the outer part of the disk. Finally, we discuss our findings in the context of competing scenarios proposed for LB-1. Further astrometric Gaia data will test between alternative solutions.
- ID:
- ivo://CDS.VizieR/J/ApJS/244/14
- Title:
- Cassini CIRS observations of Titan 2004-2017
- Short Name:
- J/ApJS/244/14
- Date:
- 28 Dec 2021 09:28:19
- Publisher:
- CDS
- Description:
- From 2004 to 2017, the Cassini spacecraft orbited Saturn, completing 127 close flybys of its largest moon, Titan. Cassini's Composite Infrared Spectrometer (CIRS), one of 12 instruments carried on board, profiled Titan in the thermal infrared (7-1000{mu}m) throughout the entire 13yr mission. CIRS observed on both targeted encounters (flybys) and more distant opportunities, collecting 8.4 million spectra from 837 individual Titan observations over 3633hr. Observations of multiple types were made throughout the mission, building up a vast mosaic picture of Titan's atmospheric state across spatial and temporal domains. This paper provides a guide to these observations, describing each type and chronicling its occurrences and global-seasonal coverage. The purpose is to provide a resource for future users of the CIRS data set, as well as those seeking to put existing CIRS publications into the overall context of the mission, and to facilitate future intercomparison of CIRS results with those of other Cassini instruments and ground-based observations.
- ID:
- ivo://CDS.VizieR/J/MNRAS/424/2442
- Title:
- Catalog of bubbles from Milky Way Project
- Short Name:
- J/MNRAS/424/2442
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a new catalogue of 5106 infrared bubbles created through visual classification via the online citizen science website The Milky Way Project. Bubbles in the new catalogue have been independently measured b at least five individuals, producing consensus parameters for their position, radius, thickness, eccentricity and position angle. Citizen scientists - volunteers recruited online and taking part in this research - have independently rediscovered the locations of at least 86 percent of three widely used catalogues of bubbles and HII regions whilst finding an order of magnitude more objects. 29 per cent of the Milky Way Project catalogue bubbles lie on the rim of a larger bubble, or have smaller bubbles located within them, opening up the possibility of better statistical studies of triggered star formation. Also outlined is the creation of a heat map of star formation activity in the Galactic plane. This online resource provides a crowd-sourced map of bubbles and arcs in the Milky Way, and will enable better statistical analysis of Galactic star formation sites.
- ID:
- ivo://CDS.VizieR/J/A+A/584/A91
- Title:
- Catalog of dense cores in Aquila from Herschel
- Short Name:
- J/A+A/584/A91
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present and discuss the results of the Herschel Gould Belt survey (HGBS) observations in an ~11deg^2^ area of the Aquila molecular cloud complex at d~260pc, imaged with the SPIRE and PACS photometric cameras in parallel mode from 70-micron to 500-micron. Using the multi-scale, multi-wavelength source extraction algorithm getsources, we identify a complete sample of starless dense cores and embedded (Class 0-I) protostars in this region, and analyze their global properties and spatial distributions. We find a total of 651 starless cores, ~60% +/-10% of which are gravitationally bound prestellar cores, and they will likely form stars in the future. We also detect 58 protostellar cores. The core mass function (CMF) derived for the large population of prestellar cores is very similar in shape to the stellar initial mass function (IMF), confirming earlier findings on a much stronger statistical basis and supporting the view that there is a close physical link between the stellar IMF and the prestellar CMF. The global shift in mass scale observed between the CMF and the IMF is consistent with a typical star formation efficiency of ~40% at the level of an individual core. By comparing the numbers of starless cores in various density bins to the number of young stellar objects (YSOs), we estimate that the lifetime of prestellar cores is ~1Myr, which is typically ~4 times longer than the core free-fall time, and that it decreases with average core density. We find a strong correlation between the spatial distribution of prestellar cores and the densest filaments observed in the Aquila complex. About 90% of the Herschel-identified prestellar cores are located above a background column density corresponding to A_V_~7, and ~75% of them lie within filamentary structures with supercritical masses per unit length >~16M_{sun}_/pc. These findings support a picture wherein the cores making up the peak of the CMF (and probably responsible for the base of the IMF) result primarily from the gravitational fragmentation of marginally supercritical filaments. Given that filaments appear to dominate the mass budget of dense gas at A_V_>7, our findings also suggest that the physics of prestellar core formation within filaments is responsible for a characteristic "efficiency" SFR/M_dense_~5+/-2x10^-8^yr^-1^ for the star formation process in dense gas.
- ID:
- ivo://CDS.VizieR/J/A+A/638/A74
- Title:
- Catalog of dense cores in Oph molecular cloud
- Short Name:
- J/A+A/638/A74
- Date:
- 02 Mar 2022 11:56:27
- Publisher:
- CDS
- Description:
- Herschel observations of nearby clouds in the Gould Belt support a paradigm for low-mass star formation, starting with the generation of molecular filaments, followed by filament fragmentation, and the concentration of mass into self-gravitating prestellar cores. With the unique far-infrared and submillimeter continuum imaging capabilities of the Herschel Space observatory, the closeby (d=139pc) Ophiuchus cloud was mapped at five wavelengths from 70 microns to 500 microns with the aim of providing a complete census of dense cores in this region, including unbound starless cores, bound prestellar cores, and protostellar cores. Taking advantage of the high dynamic range and multi-wavelength nature of the Herschel data, we used the multi-scale decomposition algorithms getsources and getfilaments to identify a complete sample of dense cores and filaments in the cloud and study their properties. The densest clouds of the Ophiuchus complex, L1688 and L1689, which thus far are only indirectly described as filamentary regions owing to the spatial distribution of their young stellar objects (YSOs), are confirmed to be dominated by filamentary structures. The tight correlation observed between prestellar cores and filamentary structures in L1688 and L1689 supports the view that solar-type star formation occurs primarily in dense filaments. While the sub clouds of the complex show disparities, L1689 being less efficient than L1688 at forming stars when considering their total mass budgets, both sub clouds share almost the same prestellar core formation efficiency in dense molecular gas. We also find evidence in the Herschel data for a remarkable concentric geometrical configuration in L1688 which is dominated by up to three arc-like compression fronts and presumably created by shockwave events emanating from the Sco OB2 association, including the neighboring massive (O9V) star sigma Sco.
- ID:
- ivo://CDS.VizieR/J/A+A/635/A34
- Title:
- Catalog of dense cores in Orion B from Herschel
- Short Name:
- J/A+A/635/A34
- Date:
- 14 Jan 2022 08:07:23
- Publisher:
- CDS
- Description:
- We present a detailed study of the Orion B molecular cloud complex (d~400pc), which was imaged with the PACS and SPIRE photometric cameras at wavelengths from 70-micron to 500-micron as part of the Herschel Gould Belt survey (HGBS). We release new high-resolution maps of column density and dust temperature for the whole complex, derived in the same consistent manner as for other HGBS regions. In the filamentary subregions NGC2023 and 2024, NGC2068 and 2071, and L1622, a total of 1768 starless dense cores were identified based on Herschel data, 490-804 (~28-45%) of which are self-gravitating prestellar cores that will likely form stars in the future. A total of 76 protostellar dense cores were also found. The typical lifetime of the prestellar cores was estimated to be t_pre_^OrionB^=1.7(-0.6/+0.8)Myr. The prestellar core mass function (CMF) derived for the whole sample of prestellar cores peaks at ~0.5Msun (in dN/dlogM format) and is consistent with a power-law with logarithmic slope -1.27+/-0.24 at the high-mass end, compared to the Salpeter slope of -1.35. In the Orion B region, we confirm the existence of a transition in prestellar core formation efficiency (CFE) around a fiducial value A_V_^bg^~7mag in background visual extinction, which is similar to the trend observed with Herschel in other regions, such as the Aquila cloud. This is not a sharp threshold, however, but a smooth transition between a regime with very low prestellar CFE at A_V_^bg^<5 and a regime with higher, roughly constant CFE at A_V_^bg^>~10. The total mass in the form of prestellar cores represents only a modest fraction (~20%) of the dense molecular cloud gas above A_V_^bg^>~7mag. About 60-80% of the prestellar cores are closely associated with filaments, and this fraction increases up to >90% when a more complete sample of filamentary structures is considered. Interestingly, the median separation observed between nearest core neighbors corresponds to the typical inner filament width of ~0.1pc, which is commonly observed in nearby molecular clouds, including Orion B. Analysis of the CMF observed as a function of background cloud column density shows that the most massive prestellar cores are spatially segregated in the highest column density areas, and suggests that both higher- and lower-mass prestellar cores may form in denser filaments.
- ID:
- ivo://CDS.VizieR/J/ApJ/627/621
- Title:
- Catalog of Extremely Red Objects
- Short Name:
- J/ApJ/627/621
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We use a serendipitously discovered overdensity of extremely red objects (EROs) to study the morphologies and cumulative surface number density of EROs in a dense environment. Our extremely deep imaging allows us to select very faint EROs, reaching K_S_=21, or ~2mag fainter than the L* of passively evolving ellipticals at z=1.5.
