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Long-term photometric observations of pre-main sequence objects in the field of North America/Pelican Nebula
摘要： To broaden the search and study stars in the early evolutionary phase, we investigated a sample of 17 pre-main sequence objects previously detected as either Hα emission-line pre-main sequence stars or T Tauri variables located in the field of the North America/Pelican Nebula complex. Johnson-Cousins B, V, Rc, Ic magnitudes and mean color indices for the program stars are determined from more than 12 400 measurements from archive photographic plates and from CCD data collected at 7 observatories covering the period of almost 60 years from 1954 up to 2013. We complemented previously rare insights on the photometry of the program stars and presented their photometric history, which for almost all program stars is the first long term photometric monitoring on a timescale of 6 decades. Eight program stars are found to be classical T Tauri stars of variability type II, while 6 program stars are weak-line T Tauri stars of variability type I. For the first time, periodicity is found for three stars: V1716 Cyg indicates a 4.15 day period, V2051 Cyg indicates a 384 day period, and V521 Cyg a period of 503 days.
关键词： stars: pre-main sequence,stars: variables: general
更新于2025-09-23 15:22:29
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Physical properties of the jet from DG Tauri on sub-arcsecond scales with HST/STIS
摘要： Context. Stellar jets are believed to play a key role in star formation, but the question of how they originate is still being debated. Aims. We derive the physical properties at the base of the jet from DG Tau both along and across the flow and as a function of velocity. Methods. We analysed seven optical spectra of the DG Tau jet, taken with the Hubble Space Telescope Imaging Spectrograph. The spectra were obtained by placing a long-slit parallel to the jet axis and stepping it across the jet width. The resulting position-velocity diagrams in optical forbidden emission lines allowed access to plasma conditions via calculation of emission line ratios. In this way, we produced a 3D map (2D in space and 1D in velocity) of the jet's physical parameters i.e. electron density ne, hydrogen ionisation fraction xe, and total hydrogen density nH. The method used is a new version of the BE-technique. Results. A fundamental improvement is that the new diagnostic method allows us to overcome the upper density limit of the standard [S ii] diagnostics. As a result, we find at the base of the jet high electron density, ne ～ 105, and very low ionisation, xe ～ 0.02?0.05, which combine to give a total density up to nH ～ 3 × 106. This analysis confirms previous reports of variations in plasma parameters along the jet, (i.e. decrease in density by several orders of magnitude, increase of xe from 0.05 to a plateau at 0.7 downstream at 2'' from the star). Furthermore, a spatial coincidence is revealed between sharp gradients in the total density and supersonic velocity jumps. This strongly suggests that the emission is caused by shock excitation. No evidence was found of variations in the parameters across the jet, within a given velocity interval. The position-velocity diagrams indicate the presence of both fast accelerating gas and slower, less collimated material. We derive the mass outflow rate, ˙Mj, in the blue-shifted lobe in different velocity channels, that contribute to a total of ˙Mj ～ 8 ± 4× 10?9 M☉ yr?1. We estimate that a symmetric bipolar jet would transport at the low and intermediate velocities probed by rotation measurements, an angular momentum flux of ˙Lj ～ 2.9 ± 1.5 × 10?6 M☉ yr?1 AU km s?1. We discuss implications of these findings for jet launch theories. Conclusions. The derived properties of the DG Tau jet are demonstrated to be consistent with magneto-centrifugal theory. However, non-stationary modelling is required in order to explain all of the features revealed at high resolution.
关键词： ISM: jets and outflows,Herbig-Haro objects,stars: pre-main sequence,stars: formation
更新于2025-09-23 15:22:29
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The <i>Gaia</i> DR2 view of the Gamma Velorum cluster: resolving the 6D structure
摘要： Gaia-ESO Survey observations of the young Gamma Velorum cluster led to the discovery of two kinematically distinct populations, Gamma Vel A and B, respectively, with population B extended over several square degrees in the Vela OB2 association. Using the Gaia DR2 data for a sample of high-probability cluster members, we find that the two populations differ not only kinematically, but are also located at different distances along the line of sight, with the main cluster Gamma Vel A being closer. A combined fit of the two populations yields (cid:36)A = 2.895 0.011 mas 11.5 pc and 383.4+2.5+15.3 and 0.091 14.2 pc, respectively, showing that Gamma Vel A is closer than Gamma Vel B by 38 pc. We find that the two clusters are nearly coeval, and that Gamma Vel B is expanding. We suggest that Gamma Vel A and B are two independent clusters located along the same line of sight.
关键词： open clusters and associations: individual: Gamma Velorum,stars: late-type,stars: pre-main sequence,stars: distances,stars: kinematics and dynamics
更新于2025-09-23 15:21:21
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The VISTA Carina Nebula Survey
摘要： We performed a deep wide-field (6.76 sq. deg) near-infrared survey with the VISTA telescope that covers the entire extent of the Carina nebula complex (CNC). The point-source catalog created from these data contains around four million individual objects down to masses of 0.1 M(cid:3). We present a statistical study of the large-scale spatial distribution and an investigation of the clustering properties of infrared-excesses objects, which are used to trace disk-bearing young stellar objects (YSOs). A selection based on a near-infrared (J ? H) versus (H ? Ks) color–color diagram shows an almost uniform distribution over the entire observed area. We interpret this as a result of the very high degree of background contamination that arises from the Carina Nebula’s location close to the Galactic plane. Complementing the VISTA near-infrared catalog with Spitzer IRAC mid-infrared photometry improves the situation of the background contamination considerably. We find that a (J ? H) versus (Ks ? [4.5]) color–color diagram is well suited to tracing the population of YSO-candidates (cYSOs) by their infrared excess. We identify 8781 sources with strong infrared excess, which we consider as cYSOs. This sample is used to investigate the spatial distribution of the cYSOs with a nearest-neighbor analysis. The surface density distribution of cYSOs agrees well with the shape of the clouds as seen in our Herschel far-infrared survey. The strong decline in the surface density of excess sources outside the area of the clouds supports the hypothesis that our excess-selected sample consists predominantly of cYSOs with a low level of background contamination. This analysis allows us to identify 14 groups of cYSOs outside the central area.Our results suggest that the total population of cYSOs in the CNC comprises about 164 000 objects, with a substantial fraction (～35%) located in the northern, still not well studied parts. Our cluster analysis suggests that roughly half of the cYSOs constitute a non-clustered, dispersed population.
关键词： stars: formation,infrared: stars,stars: low-mass,stars: pre-main sequence,ISM: individual objects: NGC 3372
更新于2025-09-23 15:19:57
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POISSON project
摘要： Context. As part of the Protostellar Optical-Infrared Spectral Survey On NTT (POISSON) project, we present the results of the analysis of low-resolution near-IR spectroscopic data (0.9–2.4 μm) of two samples of young stellar objects in the Lupus (52 objects) and Serpens (17 objects) star-forming clouds, with masses in the range of 0.1 to 2.0 M☉ and ages spanning from 10^5 to a few 10^7 yr. Aims. After determining the accretion parameters of the targets by analysing their H i near-IR emission features, we added the results from the Lupus and Serpens clouds to those from previous regions (investigated in POISSON with the same methodology) to obtain a final catalogue (143 objects) of mass accretion rate values (?_acc) derived in a homogeneous and consistent fashion. Our final goal is to analyse how ?_acc correlates with the stellar mass (M_*) and how it evolves in time in the whole POISSON sample. Methods. We derived the accretion luminosity (L_acc) and ?_acc for Lupus and Serpens objects from the Brγ (Paβ in a few cases) line by using relevant empirical relationships available in the literature that connect the H i line luminosity and L_acc. To minimise the biases that arise from adopting literature data that are based on different evolutionary models and also for self-consistency, we re-derived mass and age for each source of the POISSON samples using the same set of evolutionary tracks. Results. We observe a correlation ?_acc ～ M_*^2.2 between mass accretion rate and stellar mass, similarly to what has previously been observed in several star-forming regions. We find that the time variation of ?_acc is roughly consistent with the expected evolution of the accretion rate in viscous disks, with an asymptotic decay that behaves as t^?1.6. However, ?_acc values are characterised by a large scatter at similar ages and are on average higher than the predictions of viscous models. Conclusions. Although part of the scattering may be related to systematics due to the employed empirical relationship and to uncertainties on the single measurements, the general distribution and decay trend of the ?_acc points are real. These findings might be indicative of a large variation in the initial mass of the disks, of fairly different viscous laws among disks, of varying accretion regimes, and of other mechanisms that add to the dissipation of the disks, such as photo-evaporation.
关键词： accretion, accretion disks,infrared: stars,stars: formation,stars: pre-main sequence,stars: evolution
更新于2025-09-19 17:15:36
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Thermal Infrared Imaging of MWC 758 with the Large Binocular Telescope: Planetary-driven Spiral Arms?
摘要： Theoretical studies suggest that a giant planet around the young star MWC 758 could be responsible for driving the spiral features in its circumstellar disk. Here, we present a deep imaging campaign with the Large Binocular Telescope with the primary goal of imaging the predicted planet. We present images of the disk in two epochs in the L′ filter (3.8 μm) and a third epoch in the M′ filter (4.8 μm). The two prominent spiral arms are detected in each observation, which constitute the first images of the disk at M′, and the deepest yet in L′ (ΔL′ = 12.1 exterior to the disk at 5σ significance). We report the detection of an S/N ～ 3.9 source near the end of the Southern arm, and, from the source’s detection at a consistent position and brightness during multiple epochs, we establish a ～90% confidence-level that the source is of astrophysical origin. We discuss the possibilities that this feature may be (a) an unresolved disk feature, and (b) a giant planet responsible for the spiral arms, with several arguments pointing in favor of the latter scenario. We present additional detection limits on companions exterior to the spiral arms, which suggest that a ?4 MJup planet exterior to the spiral arms could have escaped detection. Finally, we do not detect the companion candidate interior to the spiral arms reported recently by Reggiani et al., although forward modeling suggests that such a source would have likely been detected.
关键词： planets and satellites: formation,stars: pre-main sequence,planets and satellites: detection,planet–disk interactions
更新于2025-09-19 17:13:59
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SOFIA MID-INFRARED IMAGING AND CSO SUBMILLIMETER POLARIMETRY OBSERVATIONS OF G034.43+00.24 MM1
摘要： We present 11.1 to 37.1 μm imaging observations of the very dense molecular cloud core MM1 in G034.43+00.24 using FORCAST on SOFIA and submillimeter (submm) polarimetry using SHARP on the Caltech Submillimeter Observatory. We ?nd that at the spatial resolution of SOFIA, the point-spread function (PSF) of MM1 is consistent with being a single source, as expected based on millimeter (mm) and submm observations. The spectral energy distributions (SEDs) of MM1 and MM2 have a warm component at the shorter wavelengths not seen in mm and submm SEDs. Examination of H(1.65 μm) stellar polarimetry from the Galactic Plane Infrared Polarization Survey shows that G034 is embedded in an external magnetic ?eld aligned with the Galactic Plane. The SHARP polarimetry at 450 μm shows a magnetic ?eld geometry in the vicinity of MM1 that does not line up with either the Galactic Plane or the mean ?eld direction inferred from the CARMA interferometric polarization map of the central cloud core, but is perpendicular to the long ?lament in which G034 is embedded. The CARMA polarimetry does show evidence for grain alignment in the central region of the cloud core, and thus does trace the magnetic ?eld geometry near the embedded Class 0 YSO.
关键词： stars: formation,stars: pre-main sequence,ISM: magnetic ?elds
更新于2025-09-16 10:30:52
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The protoplanetary system HD 100546 in H <i>α</i> polarized light from SPHERE/ZIMPOL
摘要： Context. HD 100546 is one of the few known pre-main-sequence stars that may host a planetary system in its disk. Aims. This work aims to contribute to our understanding of HD 100546 by analyzing new polarimetric images with high spatial resolution. Methods. Using VLT/SPHERE/ZIMPOL with two filters in Hα and the adjacent continuum, we have probed the disk gap and the surface layers of the outer disk, covering a region <500 mas (<55 au at 109 pc) from the central star, at an angular resolution of ～20 mas. Results. Our data show an asymmetry: the SE and NW regions of the outer disk are more polarized than the SW and NE regions. This asymmetry can be explained from a preferential scattering angle close to 90? and is consistent with previous polarization images. The outer disk in our observations extends from 13 ± 2 to 45 ± 9 au, with a position angle and inclination of 137 ± 5? and 44 ± 8?, respectively. The comparison with previous estimates suggests that the disk inclination could increase with the stellocentric distance, although the different measurements are still consistent within the error bars. In addition, no direct signature of the innermost candidate companion is detected from the polarimetric data, confirming recent results that were based on intensity imagery. We set an upper limit to its mass accretion rate <10?8 M(cid:12) yr?1 for a substellar mass of 15 MJup. Finally, we report the first detection (>3σ) of a ～20 au bar-like structure that crosses the gap through the central region of HD 100546. Conclusions. In the absence of additional data, it is tentatively suggested that the bar could be dust dragged by infalling gas that radially flows from the outer disk to the inner region. This could represent an exceptional case in which a small-scale radial inflow is observed in a single system. If this scenario is confirmed, it could explain the presence of atomic gas in the inner disk that would otherwise accrete on to the central star on a timescale of a few months/years, as previously indicated from spectro-interferometric data, and could be related with additional (undetected) planets.
关键词： techniques: high angular resolution,protoplanetary disks,stars: pre-main sequence,circumstellar matter,stars: variables: T Tauri, Herbig Ae/Be,planet-disk interactions
更新于2025-09-10 09:29:36
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Mid-infrared characterization of the planetary-mass companion ROXs 42B b
摘要： We present new Keck/NIRC2 3–5 μm infrared photometry of the planetary-mass companion to ROXS 42B in L(cid:48), and for the ?rst time in Brackett-α (Brα) and in Ms-band. We combine our data with existing near-infrared photometry and K-band (2–2.4 μm) spectroscopy and compare these data with models and other directly imaged planetary-mass objects using forward modeling and retrieval methods in order to characterize the atmosphere of ROXS 42B b. The ROXS 42B b 1.25–5 μm spectral energy distribution most closely resembles that of GSC 06214 B and κ And b, although it has a slightly bluer Ks?Ms color than GSC 06214 B and thus currently lacks evidence of a circumplanetary disk. We cannot formally exclude the possibility that any of the tested dust-free/dusty/cloudy forward models describe the atmosphere of ROXS 42B b well. However, models with substantial atmospheric dust/clouds yield temperatures and gravities that are consistent when ?t to photometry and spectra separately, whereas dust-free model ?ts to photometry predict temperatures/gravities inconsistent with the ROXS 42B b K-band spectrum and vice-versa. Atmospheric retrieval on the 1–5 μm photometry places a limit on the fractional number density of CO2 of log(nCO2 ) < ?2.7, but provides no other constraints so far. We conclude that ROXS 42B b has mid-IR photometric features that are systematically di?erent from other previously observed planetary-mass and ?eld objects of similar temperature. It remains unclear whether this is in the range of the natural diversity of targets at the very young (～2 Myr) age of ROXS 42B b or unique to its early evolution and environment.
关键词： planets and satellites: detection,planets and satellites: individual: ROXS42Bb,stars: pre-main sequence
更新于2025-09-10 09:29:36
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Mapping accretion and its variability in the young open cluster NGC 2264: a study based on <i>u</i> -band photometry
摘要： Context. The accretion process has a central role in the formation of stars and planets. Aims. We aim at characterizing the accretion properties of several hundred members of the star-forming cluster NGC 2264 (3 Myr). Methods. We performed a deep ugri mapping as well as a simultaneous u-band+r-band monitoring of the star-forming region with CFHT/MegaCam in order to directly probe the accretion process onto the star from UV excess measurements. Photometric properties and stellar parameters are determined homogeneously for about 750 monitored young objects, spanning the mass range ～0.1–2 M(cid:4). About 40% of the sample are classical (accreting) T Tauri stars, based on various diagnostics (Hα, UV and IR excesses). The remaining non-accreting members de?ne the (photospheric + chromospheric) reference UV emission level over which ?ux excess is detected and measured. Results. We revise the membership status of cluster members based on UV accretion signatures, and report a new population of 50 classical T Tauri star (CTTS) candidates. A large range of UV excess is measured for the CTTS population, varying from a few times 0.1 to ～3 mag. We convert these values to accretion luminosities and accretion rates, via a phenomenological description of the accretion shock emission. We thus obtain mass accretion rates ranging from a few 10?10 to ～10?7 M(cid:4)/yr. Taking into account a mass-dependent detection threshold for weakly accreting objects, we ?nd a >6σ correlation between mass accretion rate and stellar mass. A power-law ?t, properly accounting for censored data (upper limits), yields ˙Macc ∝ M1.4±0.3. At any given stellar mass, we ?nd a large spread of accretion rates, extending over about 2 orders of magnitude. The monitoring of the UV excess on a timescale of a couple of weeks indicates that its variability typically amounts to 0.5 dex, i.e., much smaller than the observed spread in accretion rates. We suggest that a non-negligible age spread across the star-forming region may e?ectively contribute to the observed spread in accretion rates at a given mass. In addition, di?erent accretion mechanisms (like, e.g., short-lived accretion bursts vs. more stable funnel-?ow accretion) may be associated to di?erent ˙Macc regimes. Conclusions. A huge variety of accretion properties is observed for young stellar objects in the NGC 2264 cluster. While a de?nite correlation seems to hold between mass accretion rate and stellar mass over the mass range probed here, the origin of the large intrinsic spread observed in mass accretion rates at any given mass remains to be explored.
关键词： accretion,stars: pre-main sequence,stars: formation,stars: low-mass,ultraviolet: stars,open clusters and associations: individual: NGC 2264,accretion disks
更新于2025-09-04 15:30:14