Dusty Circumstellar Disk Research Articles

Decoding the X-Ray Flare from MAXI J0709–159 Using Optical Spectroscopy and Multiepoch Photometry

We present a follow-up study on the recent detection of two X-ray flaring events by MAXI/Gas Slit Camera observations in soft and hard X-rays from MAXI J0709–159 in the direction of HD 54786 (LY CMa), on 2022 January 25. The X-ray luminosity during the flare was around 1037 erg s−1 (MAXI), which got reduced to 1032 erg s−1 (NuSTAR) after the flare. We took low-resolution spectra of HD 54786 from the 2.01 m Himalayan Chandra Telescope and the 2.34 m Vainu Bappu Telescope (VBT) facilities in India, on 2022 February 1 and 2. In addition to Hα emission, we found emission lines of He i in the optical spectrum of this star. By comparing our spectrum of the object with those from the literature we found that He i lines show variability. Using photometric studies we estimate that the star has an effective temperature of 20,000 K. Although HD 54786 is reported as a supergiant in previous studies, our analysis favors it to be evolving off the main sequence in the color–magnitude diagram. We could not detect any infrared excess, ruling out the possibility of IR emission from a dusty circumstellar disk. Our present study suggests that HD 54786 is a Be/X-ray binary system with a compact object companion, possibly a neutron star.

Bridging the Gap between Protoplanetary and Debris Disks: Separate Evolution of Millimeter and Micrometer-sized Dust

Abstract The connection between the nature of a protoplanetary disk and that of a debris disk is not well understood. Dust evolution, planet formation, and disk dissipation likely play a role in the processes involved. We aim to reconcile both manifestations of dusty circumstellar disks through a study of optically thin Class III disks and how they correlate to younger and older disks. In this work, we collect literature and Atacama Large Millimeter/submillimeter Array archival millimeter fluxes for 85 disks (8%) of all Class III disks across nearby star-forming regions. We derive millimeter-dust masses M dust and compare these with Class II and debris disk samples in the context of excess infrared luminosity, accretion rate, and age. The mean M dust of Class III disks is 0.29 ± 0.19 M ⊕. We propose a new evolutionary scenario wherein radial drift is very efficient for nonstructured disks during the Class II phase resulting in a rapid M dust decrease. In addition, we find possible evidence for long infrared protoplanetary disk timescales, ∼8 Myr, consistent with overall slow disk evolution. In structured disks, the presence of dust traps allows for the formation of planetesimal belts at large radii, such as those observed in debris disks. We propose therefore that the planetesimal belts in debris disks are the result of dust traps in structured disks, whereas protoplanetary disks without dust traps decrease in dust mass through radial drift and are therefore undetectable as debris disks after the gas dissipation. These results provide a hypothesis for a novel view of disk evolution.

An ALMA Study of the FU Ori–type Object V900 Mon: Implications for the Progenitor

Abstract We present ALMA observations of 12CO, 13CO, and C18O J = 2–1 lines and the 230 GHz continuum for the FU Ori–type object (FUor) V900 Mon (d ∼ 1.5 kpc), for which the accretion burst was triggered between 1953 and 2009. We identified CO emission associated with a molecular bipolar outflow extending up to an ∼104 au scale and a rotating molecular envelope extending over >104 au. The interaction with the hot energetic FUor wind, which was observed using optical spectroscopy, appears limited to a region within ∼400 au of the star. The envelope mass and collimation of the extended CO outflow suggest that the progenitor of this FUor is a low-mass Class I young stellar object (YSO). These parameters for V900 Mon, another FUor, and a few FUor-like stars are consistent with the idea that FUor outbursts are associated with normal YSOs. The continuum emission is marginally resolved in our observations with a 0.″2 × 0.″15 (∼300 × 225 au) beam, and a Gaussian model provides a deconvolved FWHM of ∼90 au. The emission is presumably associated with a dusty circumstellar disk, plus a possible contribution from a wind or wind cavity close to the star. The warm compact nature of the disk continuum emission could be explained with viscous heating of the disk, while gravitational fragmentation in the outer disk and/or a combination of grain growth and their inward drift may also contribute to its compact nature.

Dippers and dusty disc edges: new diagnostics and comparison to model predictions

We revisit the nature of large dips in flux from extinction by dusty circumstellar material that is observed by Kepler for many young stars in the Upper Sco and $\rho$ Oph star formation regions. These young, low-mass "dipper" stars are known to have low accretion rates and primarily host moderately evolved dusty circumstellar disks. Young low mass stars often exhibit rotating star spots that cause quasi-periodic photometric variations. We found no evidence for periods associated with the dips that are different from the star spot rotation period in spectrograms constructed from the light curves. The material causing the dips in most of these light curves must be approximately corotating with the star. We find that disk temperatures computed at the disk corotation radius are cool enough that dust should not sublime. Crude estimates for stellar magnetic field strengths and accretion rates are consistent with magnetospheric truncation near the corotation radius. Magnetospheric truncation models can explain why the dips are associated with material near corotation and how dusty material is lifted out of the midplane to obscure the star which would account for the large fraction of young low mass stars that are dippers. We propose that variations in disk orientation angle, stellar magnetic field dipole tilt axis, and disk accretion rate are underlying parameters accounting for differences in the dipper light curves.

RAPID CIRCUMSTELLAR DISK EVOLUTION AND AN ACCELERATING STAR FORMATION RATE IN THE INFRARED DARK CLOUD M17 SWex

ABSTRACT We present a catalog of 840 X-ray sources and first results from a 100 ks Chandra X-ray Observatory imaging study of the filamentary infrared (IR) dark cloud G014.225–00.506, which forms the central regions of a larger cloud complex known as the M17 southwest extension (M17 SWex). In addition to the rich population of protostars and young stellar objects with dusty circumstellar disks revealed by archival data from the Spitzer Space Telescope, we discover a population of X-ray-emitting, intermediate-mass pre-main-sequence stars that lack IR excess emission from circumstellar disks. We model the IR spectral energy distributions of this source population to measure its mass function and place new constraints on the destruction timescales for the inner dust disk for 2–8 M ☉ stars. We also place a lower limit on the star formation rate (SFR) and find that it is quite high ( M ☉ yr−1), equivalent to several Orion Nebula Clusters in G14.225–0.506 alone, and likely accelerating. The cloud complex has not produced a population of massive, O-type stars commensurate with its SFR. This absence of very massive (≳20 M ☉) stars suggests that either (1) M17 SWex is an example of a distributed mode of star formation that will produce a large OB association dominated by intermediate-mass stars but relatively few massive clusters, or (2) the massive cores are still in the process of accreting sufficient mass to form massive clusters hosting O stars.

Imaging the dust sublimation front of a circumbinary disk

We present the first near-IR milli-arcsecond-scale image of a post-AGB binary that is surrounded by hot circumbinary dust. A very rich interferometric data set in six spectral channels was acquired of IRAS08544-4431 with the new RAPID camera on the PIONIER beam combiner at the Very Large Telescope Interferometer (VLTI). A broadband image in the \textit{H} band was reconstructed by combining the data of all spectral channels using the SPARCO method. We spatially separate all the building blocks of the IRAS08544-4431 system in our milliarcsecond-resolution image. Our dissection reveals a dust sublimation front that is strikingly similar to that expected in early-stage protoplanetary disks, as well as an unexpected flux signal of $\sim$4\% from the secondary star. The energy output from this companion indicates the presence of a compact circum-companion accretion disk, which is likely the origin of the fast outflow detected in H$\alpha$. Our image provides the most detailed view into the heart of a dusty circumstellar disk to date. Our results demonstrate that binary evolution processes and circumstellar disk evolution can be studied in detail in space and over time.

AN UNBIASED 1.3 mm EMISSION LINE SURVEY OF THE PROTOPLANETARY DISK ORBITING LkCa 15

The outer (>30 AU) regions of the dusty circumstellar disk orbiting the ∼2–5 Myr old, actively accreting solar analog LkCa 15 are known to be chemically rich, and the inner disk may host a young protoplanet within its central cavity. To obtain a complete census of the brightest molecular line emission emanating from the LkCa 15 disk over the 210–270 GHz (1.4–1.1 mm) range, we have conducted an unbiased radio spectroscopic survey with the Institute de Radioastronomie Millimétrique (IRAM) 30 m telescope. The survey demonstrates that in this spectral region, the most readily detectable lines are those of CO and its isotopologues 13CO and C18O, as well as HCO+, HCN, CN, C2H, CS, and H2CO. All of these species had been previously detected in the LkCa 15 disk; however, the present survey includes the first complete coverage of the CN (2–1) and C2H (3–2) hyperfine complexes. Modeling of these emission complexes indicates that the CN and C2H either reside in the coldest regions of the disk or are subthermally excited, and that their abundances are enhanced relative to molecular clouds and young stellar object environments. These results highlight the value of unbiased single-dish line surveys in guiding future high-resolution interferometric imaging of disks.

ASPITZERVIEW OF THE GIANT MOLECULAR CLOUD MON OB1 EAST/NGC 2264

We present Spitzer 3.6, 4.5, 5.8, 8.0, and 24 micron images of the Mon OB1 East giant molecular cloud, which contains the young star forming region NGC 2264, as well as more extended star formation. With Spitzer data and 2MASS photometry, we identify and classify young stellar objects (YSOs) with dusty circumstellar disks and/or envelopes in Mon OB1 East by their infrared-excess emission and study their distribution with respect to cloud material. We find a correlation between the local surface density of YSOs and column density of molecular gas as traced by dust extinction that is roughly described as a power law in these quantities. NGC 2264 follows a power law index of ~2.7, exhibiting a large YSO surface density for a given gas column density. Outside of NGC 2264 where the surface density of YSOs is lower, the power law is shallower and the region exhibits a larger gas column density for a YSO surface density, suggesting the star formation is more recent. In order to measure the fraction of cloud members with circumstellar disks/envelopes, we estimate the number of diskless pre-main sequence stars by statistical removal of background star detections. We find that the disk fraction of the NGC 2264 region is 45%, while the surrounding more distributed regions show a disk fraction of 19%. This may be explained by the presence an older, more dispersed population of stars. In total, the Spitzer observations provide evidence for heterogenous, non-coeval star formation throughout the Mon OB1 cloud.

Spectral observations of ɛ aurigae during the 2009–2011 eclipse

The results of the spectral observations of a unique eclipsing system {\epsilon} Aurigae obtained during the recent eclipse are presented. We traced the spectral lines variations at different eclipse phases. The part of these changes is the result of the absorption of stellar radiation by the gas component of circumstellar (CS) disk around the secondary. The other part arises due to the obscuration of the stellar photosphere and the closest circumstellar area by the dusty CS disk. Comparison of our results with the previous one, obtained by Lambert & Sawyer during the 1982-1984 eclipse, indicates the good agreement, and argues in favor of stability of the secondary disk structure. On the base of the new observational data we provide a new mass estimation of the system components.

IDENTIFYING NEARBY, YOUNG, LATE-TYPE STARS BY MEANS OF THEIR CIRCUMSTELLAR DISKS

It has recently been shown that a significant fraction of late-type members of nearby, very young associations (age <10 Myr) display excess emission at mid-IR wavelengths indicative of dusty circumstellar disks. We demonstrate that the detection of mid-IR excess emission can be utilized to identify new nearby, young, late-type stars including two definite new members ("TWA 33" and "TWA 34") of the TW Hydrae Association. Both new TWA members display mid-IR excess emission in the Wide-field Infrared Survey Explorer (WISE) catalog and they show proper motion and youthful spectroscopic characteristics -- namely H\alpha emission, strong lithium absorption, and low surface gravity features consistent with known TWA members. We also detect mid-IR excess -- the first unambiguous evidence of a dusty circumstellar disk -- around a previously identified UV-bright, young, accreting star (2M1337) that is a likely member of the Lower-Centaurus Crux region of the Scorpius Centaurus Complex.

Determining the Origin of Inner Planetary System Debris Orbiting the Dustiest Main Sequence Stars

AbstractWe develop a means to distinguish between warm dusty circumstellar debris disks produced by steady state collisional evolution of a planetesimal belt or through transient events.

TW HYA ASSOCIATION MEMBERSHIP AND NEWWISE-DETECTED CIRCUMSTELLAR DISKS

We assess the current membership of the nearby, young TW Hydrae Association and examine newly proposed members with the Wide-field Infrared Survey Explorer (WISE) to search for infrared excess indicative of circumstellar disks. Newly proposed members TWA 30A, TWA 30B, TWA 31, and TWA 32 all show excess emission at 12 and 22 \mum providing clear evidence for substantial dusty circumstellar disks around these low-mass, ~8 Myr old stars that were previously shown to likely be accreting from circumstellar material. TWA 30B shows large amounts of self-extinction, likely due to an edge-on disk geometry. We also confirm previously reported circumstellar disks with WISE, and determine a 22 \mum excess fraction of 42+/- 9% based on our results.

Rapid disappearance of a warm, dusty circumstellar disk

Stars form with gaseous and dusty circumstellar envelopes, which rapidly settle into disks that eventually give rise to planetary systems. Understanding the process by which these disks evolve is paramount in developing an accurate theory of planet formation that can account for the variety of planetary systems discovered so far. The formation of Earth-like planets through collisional accumulation of rocky objects within a disk has mainly been explored in theoretical and computational work in which post-collision ejecta evolution typically is ignored, although recent work has considered the fate of such material. Here we report observations of a young, Sun-like star (TYC 8241 2652 1) where infrared flux from post-collisional ejecta has decreased drastically, by a factor of about 30, over a period of less than two years. The star seems to have gone from hosting substantial quantities of dusty ejecta, in a region analogous to where the rocky planets orbit in the Solar System, to retaining at most a meagre amount of cooler dust. Such a phase of rapid ejecta evolution has not been previously predicted or observed, and no currently available physical model satisfactorily explains the observations.

MULTIPLICITY, DISKS, AND JETS IN THE NGC 2071 STAR-FORMING REGION

We present centimeter and millimeter observations of the NGC 2071 star-forming region performed with the VLA and CARMA. We detected counterparts at 3.6 cm and 3 mm for the previously known sources IRS 1, IRS 2, IRS 3, and VLA 1. All these sources show SEDs dominated by free-free thermal emission at cm wavelengths, and thermal dust emission at mm wavelengths, suggesting that all of them are associated with YSOs. IRS 1 shows a complex morphology at 3.6 cm, with changes in the direction of its elongation. We discuss two possible explanations to this morphology: the result of changes in the direction of a jet due to interactions with a dense ambient medium, or that we are actually observing the superposition of two jets arising from two components of a binary system. Higher angular resolution observations at 1.3 cm support the second possibility, since a double source is inferred at this wavelength. IRS 3 shows a clear jet-like morphology at 3.6 cm. Over a time-span of four years, we observed changes in the morphology of this source that we interpret as due to ejection of ionized material in a jet. The emission at 3 mm of IRS 3 is angularly resolved, with a deconvolved size (FWHM) of ~120 AU, and seems to be tracing a dusty circumstellar disk perpendicular to the radio jet. An irradiated accretion disk model around an intermediate-mass YSO can account for the observed SED and spatial intensity profile at 3 mm, supporting this interpretation.

A PAN-CARINA YOUNG STELLAR OBJECT CATALOG: INTERMEDIATE-MASS YOUNG STELLAR OBJECTS IN THE CARINA NEBULA IDENTIFIED VIA MID-INFRARED EXCESS EMISSION

We present a catalog of 1439 young stellar objects (YSOs) spanning the 1.42 deg^2 field surveyed by the Chandra Carina Complex Project (CCCP), which includes the major ionizing clusters and the most active sites of ongoing star formation within the Great Nebula in Carina. Candidate YSOs were identified via infrared (IR) excess emission from dusty circumstellar disks and envelopes, using data from the Spitzer Space Telescope Vela--Carina survey and the Two-Micron All Sky Survey. We model the 1--24 /mu m IR spectral energy distributions of the YSOs to constrain physical properties. Our Pan-Carina YSO Catalog (PCYC) is dominated by intermediate-mass (2 Msun < m < 10 Msun) objects with disks, including Herbig Ae/Be stars and their less evolved progenitors. The PCYC provides a valuable complementary dataset to the CCCP X-ray source catalogs, identifying 1029 YSOs in Carina with no X-ray detection. We also catalog 410 YSOs with X-ray counterparts, including 62 candidate protostars. Candidate protostars with X-ray detections tend to be more evolved than those without. In most cases, X-ray emission apparently originating from intermediate-mass, disk-dominated YSOs is consistent with the presence of low-mass companions, but we also find that X-ray emission correlates with cooler stellar photospheres and higher disk masses. We suggest that intermediate-mass YSOs produce X-rays during their early pre-main sequence evolution, perhaps driven by magnetic dynamo activity during the convective atmosphere phase, but this emission dies off as the stars approach the main sequence. Extrapolating over the stellar initial mass function scaled to the PCYC population, we predict a total population of >2x10^4 YSOs and a present-day star formation rate (SFR) of >0.008 Msun/yr. The global SFR in the Carina Nebula, averaged over the past ~5 Myr, has been approximately constant.

The Galactic unclassified B[e] star HD 50138

HD 50138 is a southern star that presents the B[e] phenomenon, but its evolutionary stage is still not well known. This object presents spectral variability, which can be explained by outbursts or shell phases and spectropolarimetric observations have shown the presence of a non-spherically symmetric circumstellar environment that is responsible for the B[e] phenomenon. Based on recent optical long baseline interferometric observations from the VLTI/MIDI and VLTI/AMBER, and also from the Keck segment-tilting experiment, we study the structure of the circumstellar environment of HD 50138, through a geometrical analytical modeling, also using the recent LITpro software and considering a large space of parameters. We resolve and describe its circumstellar geometry for the first time in detail. The presence of a dusty circumstellar disk with an orientation onto the sky-plane of 71+-7 degrees, which is perpendicular to the polarimetric measurements from the literature, was derived. We also derived that HD 50138 is seen under an intermediate angle related to the line of sight, 56+-4 degrees. In addition, the structure of the disk and the flux contributions of the gas and dust components is discussed.

PROTOPLANETARY DISK STRUCTURES IN OPHIUCHUS. II. EXTENSION TO FAINTER SOURCES

We present new results from a significant extension of our previous high angular resolution (0.3" = 40 AU) Submillimeter Array survey of the 880 um continuum emission from dusty circumstellar disks in the ~1 Myr-old Ophiuchus star-forming region. An expanded sample is constructed to probe disk structures that emit significantly lower millimeter luminosities (hence dust masses), down to the median value for T Tauri stars. Using a Monte Carlo radiative transfer code, the millimeter visibilities and broadband spectral energy distribution for each disk are simultaneously reproduced with a two-dimensional parametric model for a viscous accretion disk. We find wide ranges of characteristic radii (14-198 AU) and disk masses (0.004-0.143 M_sun), but a narrow distribution of surface density gradients (0.4-1.1) that is consistent with a uniform value $\gamma$ = 0.9 +/- 0.2 and independent of mass (or millimeter luminosity). In this sample, we find a correlation between the disk luminosity/mass and characteristic radius, such that fainter disks are both smaller and less massive. We suggest that this relationship is an imprint of the initial conditions inherited by the disks at their formation epoch, compare their angular momenta with those of molecular cloud cores, and speculate on how future observations can help constrain the distribution of viscous evolution timescales. No other correlations between disk and star properties are found. The inferred disk structures are briefly compared with theoretical models for giant planet formation, although resolution limitations do not permit us to directly comment on material inside R = 20 AU. However, there is some compelling evidence for dust evolution in the planet formation region: 4/17 disks in the sample show resolved regions of significantly reduced optical depths within ~20-40 AU of their central stars.

IPHAS A-type Stars with Mid-IR Excesses in Spitzer Surveys

AbstractThe Isaac Newton Photometric H-Alpha Survey (IPHAS) provides (r′-Hα)-(r′-i′) colors, which can be used to select AV0-5 Main Sequence star candidates (age~20-200 Myr). By combining a sample of 23050 IPHAS-selected A-type stars with 2MASS, GLIMPSE and MIPSGAL photometry we searched for mid-infrared excesses attributable to dusty circumstellar disks. Positional cross-correlation yielded a sample of 2692 A-type stars, of which 0.6% were found to have 8-μm excesses above the expected photospheric values. The low fraction of main sequence stars with mid-IR excesses found in this work indicates that dust disks in the terrestrial planet zone of Main Sequence intermediate mass stars are rare. Dissipation mechanisms such as photo-evaporation, grain growth, collisional grinding or planet formation could possibly explain the depletion of dust detected in the inner regions of these disks.

A RING/DISK/OUTFLOW SYSTEM ASSOCIATED WITH W51 NORTH: A VERY MASSIVE STAR IN THE MAKING

Sensitive and high angular resolution ($\sim$ 0.4\arcsec) SO$_2$[22$_{2,20}$ $\to$ 22$_{1,21}$] and SiO[5$\to$4] line and 1.3 and 7 mm continuum observations made with the Submillimeter Array (SMA) and the Very Large Array (VLA) towards the young massive cluster W51 IRS2 are presented. We report the presence of a large (of about 3000 AU) and massive (40 M$_\odot$) dusty circumstellar disk and a hot gas molecular ring around a high-mass protostar or a compact small stellar system associated with W51 North. The simultaneous observations of the silicon monoxide molecule, an outflow gas tracer, further revealed a massive (200 M$_\odot$) and collimated ($\sim14^\circ$) outflow nearly perpendicular to the dusty and molecular structures suggesting thus the presence of a single very massive protostar with a bolometric luminosity of more than 10$^5$ L$_\odot$. A molecular hybrid LTE model of a Keplerian and infalling ring with an inner cavity and a central stellar mass of more than 60 M$_\odot$ agrees well with the SO$_2$[22$_{2,20}$ $\to$ 22$_{1,21}$] line observations. Finally, these results suggest that mechanisms, such as mergers of low- and intermediate- mass stars, might be not necessary for forming very massive stars.

Molecules in the circumstellar disk orbiting BP Piscium

Context. BP Psc is a puzzling late-type, emission-line field star with large infrared excess. The star is encircled and enshrouded by a nearly edge-on, dusty circumstellar disk, and displays an extensive jet system similar to those associated with pre-main sequence (pre-MS) stars. However, the photospheric absorption features of the star itself appear more consistent with post-main sequence status. Aims. We seek to characterize the molecular gas component of the BP Psc disk, so as to compare the properties of its molecular disk with those of well-studied pre-main sequence stars. Methods. We conducted a mm-wave molecular line survey of BP Psc with the 30 m telescope of the Institut de Radio Astronomie Millimetrique (IRAM). We use these data to investigate the kinematics, gas mass, and chemical constituents of the BP Psc disk. Results. We detected lines of 12 CO and 13 CO and, possibly, very weak emission from HCO + and CN; HCN, H 2 CO, and SiO are not detected. The CO line profiles of BP Psc are well fit by a model invoking a disk in Keplerian rotation. The mimumum disk gas mass, inferred from the 12 CO line intensity and 13 CO/ 12 CO line ratio, is ∼0.1 Jupiter masses. Conclusions. The weakness of HCO + and CN (relative to 13 CO) stands in sharp contrast to the strong HCO+ and CN emission that characterizes most low-mass, pre-main sequence stars that have been the subjects of molecular emission-line surveys, and is suggestive of a very low level of X-ray-induced molecular ionization within the BP Psc disk. These results lend some support to the notion that BP Psc is an evolved star whose circumstellar disk has its origins in a catastrophic interaction with a close companion.