We have performed a survey for new members of the Ophiuchus cloud complex using high-precision astrometry from the second data release of Gaia, proper motions measured with multi-epoch images from the Spitzer Space Telescope, and color-magnitude diagrams constructed with photometry from various sources. Through spectroscopy of candidates selected with those data, we have identified 155 new young stars. Based on available measurements of kinematics, we classify 102, 47, and six of those stars as members of Ophiuchus, Upper Sco, and other populations in Sco-Cen, respectively. We have also assessed the membership of all other stars in the vicinity of Ophiuchus that have spectroscopic evidence of youth from previous studies, arriving at a catalog of 373 adopted members of the cloud complex. For those adopted members, we have compiled mid-IR photometry from Spitzer and the Wide-field Infrared Survey Explorer} and have used mid-IR colors to identify and classify circumstellar disks. We find that 210 of the members show evidence of disks, including 48 disks that are in advanced stages of evolution. Finally, we have estimated the relative median ages of the populations near the Ophiuchus clouds and the surrounding Upper Sco association using absolute K-band magnitudes (M_K) based on Gaia} parallaxes. If we adopt an age 10 Myr for Upper Sco, then the relative values of M_K imply median ages of ~2 Myr for L1689 and embedded stars in L1688, 3-4 Myr for low-extinction stars near L1688, and ~6 Myr for the group containing rho Oph.
We investigate the internal and relative motions of the Taurus and Ophiuchus star-forming regions using a sample of young stars with accurately measured radial velocities and proper motions. We find no evidence for expansion or contraction of the Taurus complex, but a clear indication for a global rotation, resulting in velocity gradients, this suggests a common origin, possibly related to that of Gould's Belt.
We present APEX 218 GHz observations of molecular emission in a complete sample of embedded protostars in the Ophiuchus star-forming region. To study the physical properties of the cores, we calculate H$_2$CO and c-C$_3$H$_2$ rotational temperatures, both of which are good tracers of the kinetic temperature of the molecular gas. We find that the H$_2$CO temperatures range between 16 K and 124 K, with the highest H$_2$CO temperatures toward the hot corino source IRAS 16293-2422 (69-124 K) and the sources in the $ρ$ Oph A cloud (23-49 K) located close to the luminous Herbig Be star S 1, which ex…
We present the results of an optical photometry and high-resolution spectroscopy campaign for a modest sample of X-ray selected stars in the Chamaeleon and Rho Ophiuchus star forming regions. With R~50000 optical spectra, we establish kinematic membership of the parent association and confirm stellar youth for each star in our sample. With the acquisition of new standardized BVIc photometry, in concert with near-infrared data from the literature, we derive age and mass from stellar positions in model-dependent Hertzsprung-Russell diagrams. We compare isochronal ages derived using colour-depend…
We present spatial and kinematic correlation between the young stellar population and the cloud clumps in the Ophiuchus star-forming region. The stellar sample consists of known young objects at various evolutionary stages, taken from the literature, some of which are diagnosed with Gaia EDR3 parallax and proper-motion measurements. The molecular gas is traced by the 850 $μ$m Submillimetre Common-User Bolometer Array-2 image, reaching $\sim$2.3 mJy beam$^{-1}$, the deepest so far for the region, stacked from the James Clerk Maxwell Telescope/Transient program aiming to detect submillimeter out…
The study of the properties of disks around young brown dwarfs can provide important clues on the formation of these very low-mass objects and on the possibility of forming planetary systems around them. The presence of warm dusty disks around brown dwarfs is well known, based on near- and mid-infrared studies. High angular resolution observations of the cold outer disk are limited; we used ALMA to attempt a first survey of young brown dwarfs in the $ρ$-Oph star-forming region. All 17 young brown dwarfs in our sample were observed at 890 $μ$m in the continuum at $\sim0.\!^{\prime\prime}5$ angu…
We conduct a multiplicity survey of members of the rho Ophiuchus cloud complex with high resolution imaging to characterize the multiple star population of this nearby star forming region and investigate the relation between stellar multiplicity and star and planet formation. Our aperture masking survey reveals the presence of 5 new stellar companions beyond the reach of previous studies, but does not result in the detection of any new substellar companions. We find that 43+/-6% of the 114 stars in our survey have stellar mass companions between 1.3-780AU, while 7 (+8 -5)% host brown dwarf com…
We present the results of ALMA band 7 observations of dust and CO gas in the disks around 7 objects with spectral types ranging between M5.5 and M7.5 in Upper Scorpius OB1, and one M3 star in Ophiuchus. We detect unresolved continuum emission in all but one source, and the $^{12}$CO J=3-2 line in two sources. We constrain the dust and gas content of these systems using a grid of models calculated with the radiative transfer code MCFOST, and find disk dust masses between 0.1 and 1 M$_\oplus$, suggesting that the stellar mass / disk mass correlation can be extrapolated for brown dwarfs with mass…
A JWST, ALMA and VLA survey of the Ophiuchus-A star-forming region: Unveiling hidden dust mass and connecting infrared outflows to their radio origins
University of Leeds（利兹大学）；Universitat de Barcelona（巴塞罗那大学）；Institut d’Estudis Espacials de Catalunya（加泰罗尼亚空间研究所）；National Sun Yat-Sen University（国立中山大学）；National Taiwan Normal University（国立台湾师范大学）；Jet Propulsion Laboratory, California Institute of Technology（加州理工学院喷气推进实验室）
We have simulated star formation in prestellar cores, using SPH and initial conditions informed by observations of the cores in Ophiuchus. Because the observations are limited to two spatial dimensions plus radial velocity, we cannot infer initial conditions for the collapse of a particular core. However, with a minimum of assumptions (isotropic turbulence with a power-law spectrum, a thermal mix of compressive and solenoidal modes, a critical Bonnor-Ebert density profile) we can generate initial conditions that match, in a statistical sense, the distributions of mass, projected size and aspec…
On the basis of various data such as ALMA, JVLA, Chandra, {\it Herschel}, and {\it Spitzer}, we confirmed that two protostellar candidates in Oph-A are bona fide protostars or proto-brown dwarfs (proto-BDs) in extremely early evolutionary stages. Both objects are barely visible across infrared (IR, i.e., near-IR to far-IR) bands. The physical nature of the cores is very similar to that expected in first hydrostatic cores (FHSCs), objects theoretically predicted in the evolutionary phase prior to stellar core formation with gas densities of $\sim$ 10$^{11-12}$ cm$^{-3}$. This suggests that the …
Anomalies among the daughter nuclei of the extinct short-lived radionuclides (SLRs) in the calcium-aluminum-rich inclusions (CAIs) indicate that the Solar System must have been born near a source of the SLRs so that they could be incorporated before they decayed away. $γ$-rays from one such living SLR, $^{26}$Al, are detected in only a few nearby star-forming regions. Here we employ multi-wavelength observations to demonstrate that one such region, Ophiuchus, containing many pre-stellar cores that may serve as analogs for the emerging Solar System, is inundated with $^{26}$Al from the neighbor…
We present the discovery of a planetary-mass companion to CFHTWIR-Oph 98, a low-mass brown dwarf member of the young Ophiuchus star-forming region, with a wide 200-au separation (1.46 arcsec). The companion was identified using Hubble Space Telescope images, and confirmed to share common proper motion with the primary using archival and new ground-based observations. Based on the very low probability of the components being unrelated Ophiuchus members, we conclude that Oph 98 AB forms a binary system. From our multi-band photometry, we constrain the primary to be an M9-L1 dwarf, and the faint …
Far-infrared and (sub)millimeter fluxes can be used to study dust in protoplanetary disks, the building blocks of planets. Here, we combine observations from the Herschel Space Observatory with ancillary data of 284 protoplanetary disks in the Taurus, Chamaeleon I, and Ophiuchus star-forming regions, covering from the optical to mm/cm wavelengths. We analyze their spectral indices as a function of wavelength and determine their (sub)millimeter slopes when possible. Most disks display observational evidence of grain growth, in agreement with previous studies. No correlation is found between oth…
We report new dynamical masses for 5 pre-main sequence (PMS) stars in the L1495 region of the Taurus star-forming region (SFR) and 6 in the L1688 region of the Ophiuchus SFR. Since these regions have VLBA parallaxes these are absolute measurements of the stars' masses and are independent of their effective temperatures and luminosities. Seven of the stars have masses $<0.6$ solar masses, thus providing data in a mass range with little data, and of these, 6 are measured to precision $< 5 \%$. We find 8 stars with masses in the range 0.09 to 1.1 solar mass that agree well with the current genera…
We analyze samples of Spitzer Infrared Spectrograph (IRS) spectra of T Tauri stars in the Ophiuchus, Taurus, and Chamaeleon I star-forming regions, whose median ages lie in the <1 to 2 Myr range. The median mid-infrared spectra of objects in these three regions are similar in shape, suggesting, on average, similar disk structures. When normalized to the same stellar luminosity, the medians follow each other closely, implying comparable mid-infrared excess emission from the circumstellar disks. We use the spectral index between 13 and 31 micron and the equivalent width of the 10 micron silicate…
The 200-300 GHz Survey for 18 Class II Disks in the Ophiuchus Star-Forming Complex
National Sun Yat-Sen University（国立中山大学）；Johns Hopkins University（约翰斯·霍普金斯大学）；Center of Astronomy and Gravitation, National Taiwan Normal University（国立台湾师范大学天文与引力研究中心）；National Astronomical Observatories, Chinese Academy of Sciences（中国科学院国家天文台）；University of Chinese Academy of Sciences（中国科学院大学）；Center for Astrophysics | Harvard & Smithsonian（哈佛-史密森天体物理中心）；Department of Astronomy, University of California, Berkeley（加州大学伯克利分校天文学系）
We report the serendipitous discovery of an elliptical shell of CO associated with the faint stellar object SSTc2d J163134.1-24006 as part of the "Ophiuchus Disk Survey Employing ALMA" (ODISEA), a project aiming to study the entire population of protoplanetary disks in the Ophiuchus Molecular Cloud from 230 GHz continuum emission and $^{12}$CO (J=2-1), $^{13}$CO (J=2-1) and C$^{18}$CO (J=2-1) lines readable in Band-6. Remarkably, we detect a bright $^{12}$CO elliptical shape emission of $\sim$ 3$^{"}$ $\times$ 4$^{"}$ towards SSTc2d J163134.1-24006 without a 230 GHz continuum detection. Based …
The recently discovered exoplanets in binary or higher-order multiple stellar systems sparked a new interest in the study of proto-planetary discs in stellar aggregations. Here we focus on disc solids, as they make up the reservoir out of which exoplanets are assembled and dominate (sub-)millimetre disc observations. These observations suggest that discs in binary systems are fainter and smaller than in isolated systems. In addition, disc dust sizes are consistent with tidal truncation only if they orbit very eccentric binaries. In a previous study we showed that the presence of a stellar comp…
We present measurements of the orbital positions and flux ratios of 17 binary and triple systems in the Ophiuchus star forming region and the Upper Centaurus-Lupus cluster based on adaptive optics imaging at the Keck Observatory. We report the detection of visual companions in MML 50 and MML 53 for the first time, as well as the possible detection of a third component in WSB 21. For six systems in our sample, our measurements provide a second orbital position following their initial discoveries over a decade ago. For eight systems with sufficient orbital coverage, we analyze the range of orbit…
The accuracy of masses of pre-main sequence (PMS) stars derived from their locations on the Hertzsprung-Russell Diagram (HRD) can be tested by comparison with accurate and precise masses determined independently. We present 29 single stars in the Taurus star-forming region (SFR) and 3 in the Ophiuchus SFR with masses measured dynamically to a precision of at least $10 \%$. Our results include 9 updated mass determinations and 3 that have not had their dynamical masses published before. This list of stars with fundamental, dynamical masses, M$_{dyn}$, is drawn from a larger list of 39 targets i…
This thesis is part of a large ongoing effort to determine the distance and structure of all star-forming regions within several hundred parsecs of the Sun using radio-interferometric observations. The main goals of this thesis were: (1) Find the mean distance to the two best-studied nearby regions of low-mass star-formation (Taurus and Ophiuchus) with accuracies (a few percent or better) one to two orders of magnitude better than the present values, (2) Explore the structure and dynamics of these star-forming regions, and (3) Study the stars themselves.
We present the design and implementation of a medium-band near-IR filter tailored for detecting low-mass stars and brown dwarfs from the summit of Maunakea. The W-band filter is centered at 1.45 micron with a bandpass width of 6%, designed to measure the depth of the H2O water absorption prominent in objects with spectral types of M6 and later. When combined with standard J- and H-band photometry, the W-band filter is designed to determine spectral types to $\approx$1.4 subtypes for late-M and L dwarfs, largely independent of surface gravity and reddening. This filter's primary application is …
We have collated multiplicity data for five clusters (Taurus, Chamaeleon I, Ophiuchus, IC348, and the Orion Nebula Cluster). We have applied the same mass ratio (flux ratios of delta K <= 2.5) and primary mass cuts (~0.1-3.0 Msun) to each cluster and therefore have directly comparable binary statistics for all five clusters in the separation range 62-620 au, and for Taurus, Chamaeleon I, and Ophiuchus in the range 18-830 au. We find that the trend of decreasing binary fraction with cluster density is solely due to the high binary fraction of Taurus, the other clusters show no obvious trend ove…
We present the results of an age determination study for pre-main sequence stars in the Ophiuchus molecular cloud. The ages of eight pre-main sequence stars were estimated from surface gravities derived from high-resolution spectroscopy. The average age of the target stars was 0.7 Myr. By comparing the individual age and the near-infrared color excess, we found that color excess decreases gradually with a constant rate and the lifetime of the inner disk was determined to be 1.2 Myr. The estimated lifetime is nearly a half of the time compared to that of the pre-main sequence stars in the Tauru…
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 = 139 pc) Ophiuchus cloud was mapped at five wavelengths from 70 $μm$ to 500 $μm$ with the aim of providing a complete census of dense cores in this region, including unbound starless cores, bound prestellar …
Lomax et al. have constructed an ensemble of 60 prestellar cores having masses, sizes, projected shapes, temperatures and non-thermal radial velocity dispersions that match, statistically, the cores in Ophiuchus; and have simulated the evolution of these cores using SPH. Each core has been evolved once with no radiative feedback from stars, once with continuous radiative feedback, and once with episodic radiative feedback. Here we analyse the multiplicity statistics from these simulations. With episodic radiative feedback, (i) the multiplicity frequency is ~60% higher than in the field; (ii) t…
We report the orbital parameters for ROXR1 14 and RX J1622.7-2325Nw, two young, low-mass, and double-lined spectroscopic binaries recently discovered in the Ophiuchus star forming region. Accurate orbital solutions were determined from over a dozen high-resolution spectra taken with the Keck II and Gemini South telescopes. These objects are T Tauri stars with mass ratios close to unity and periods of ~5 and ~3 days, respectively. In particular, RX J1622.7-2325Nw shows a non-circularized orbit with an eccentricity of 0.30, higher than any other short-period pre-main sequence spectroscopic binar…
We used the Immersion GRating Infrared Spectrometer (IGRINS) to determine fundamental parameters for 61 K- and M-type young stellar objects (YSOs) located in the Ophiuchus and Upper Scorpius star-forming regions. We employed synthetic spectra and a Markov chain Monte Carlo approach to fit specific K-band spectral regions and determine the photospheric temperature ($T_{\rm eff}$), surface gravity ($\log$ g), magnetic field strength (B), projected rotational velocity ($v \sin i$), and K-band veiling ($r_{\rm K}$). We determined B for $\sim$46% of our sample. Stellar parameters were compared to t…
We present large-scale ($\sim$ 2000 square arcminutes), deep ($\sim$ 20 $μ$Jy), high-resolution ($\sim$ 1$''$) radio observations of the Ophiuchus star-forming complex obtained with the Karl G.\ Jansky Very Large Array at $λ$ = 4 and 6 cm. In total, 189 sources were detected, 56 of them associated with known young stellar sources, and 4 with known extragalactic objects; the other 129 remain unclassified, but most of them are most probably background quasars. The vast majority of the young stars detected at radio wavelengths have spectral types K or M, although we also detect 4 objects of A/F/B…
Context: A rich population of low-mass brown dwarfs and isolated planetary mass objects has been reported recently in the Upper Scorpius and Ophiuchus star forming complex. Aims: We investigate the membership, nature and properties of 17 of these isolated planetary mass candidates using low-resolution near-infrared spectra. Methods: We investigate the membership by looking for evidences of youth using four diagnostics: the slope of the continuum between the J and Ks band, the Hcont and TLI-g gravity sensitive indices, and by comparing the spectra to young and field (old) M and L-dwarf standard…
As protostars evolve from optically faint / infrared bright (Class I) sources to optically bright / infrared faint (Class II) the solid material in their surrounding disks accumulates into planetesimals and protoplanets. The nearby, young Ophiuchus star-forming region contains hundreds of protostars in a range of evolutionary states. Using the Atacama Large Millimeter Array to observe their millimeter continuum emission, we have measured masses of, or placed strong upper limits on, the dust content of 279 disks. The masses follow a log-normal distribution with a clear trend of decreasing mass …
The Ophiuchus cloud complex is one of the best laboratories to study the earlier stages of the stellar and protoplanetary disc evolution. The wealth of accurate astrometric measurements contained in the Gaia Data Release 2 can be used to update the census of Ophiuchus member candidates. We seek to find potential new members of Ophiuchus and identify those surrounded by a circumstellar disc. We constructed a control sample composed of 188 bona fide Ophiuchus members. Using this sample as a reference we applied three different density-based machine learning clustering algorithms (DBSCAN, OPTICS,…
The Gaia ESO Public Spectroscopic Survey (GES) is providing the astronomical community with high-precision measurements of many stellar parameters including radial velocities (RVs) of stars belonging to several young clusters and star-forming regions. One of the main goals of the young cluster observations is to study of their dynamical evolution and provide insight into their future, revealing if they will eventually disperse to populate the field, rather than evolve into bound open clusters. In this paper we report the analysis of the dynamical state of L1688 in the $ρ$~Ophiuchi molecular cl…
We report on initial results from a Spitzer program to search for very low-mass brown dwarfs in Ophiuchus. This program is an extension of an earlier study by Allers et al. which had resulted in an extraordinary success rate, 18 confirmed out of 19 candidates. Their program combined near-infrared and Spitzer photom- etry to identify objects with very cool photospheres together with circumstellar disk emission to indicate youth. Our new program has obtained deep IRAC pho- tometry of a 0.5 deg2 field that was part of the original Allers et al. study. We report 18 new candidates whose luminositie…
We have analyzed Atacama Large Millimeter/submillimeter Array (ALMA) Cycle 4 Band 6 data toward two young stellar objects (YSOs), Oph-emb5 and Oph-emb9, in the Ophiuchus star-forming region. The YSO Oph-emb5 is located in a relatively quiescent region, whereas Oph-emb9 is irradiated by a nearby bright Herbig Be star. Molecular lines from $cyclic$-C$_{3}$H$_{2}$ ($c$-C$_{3}$H$_{2}$), H$_{2}$CO, CH$_{3}$OH, $^{13}$CO, C$^{18}$O, and DCO$^{+}$ have been detected from both sources, while DCN is detected only in Oph-emb9. Around Oph-emb5, $c$-C$_{3}$H$_{2}$ is enhanced at the west side, relative to…
The formation of spectroscopic binaries (SB) may be a natural byproduct of star formation. The early dynamical evolution of multiple stellar systems after the initial fragmentation of molecular clouds leaves characteristic imprints on the properties of young, multiple stars. The discovery and the characterization of the youngest SB will allow us to infer the mechanisms and timescales involved in their formation. Our work aims to find spectroscopic companions around young stellar objects (YSO). We present a near-IR high-resolution (R ~ 60000) multi-epoch radial velocity survey of 7 YSO in the s…
Multi-epoch radio-interferometric observations of young stellar objects can be used to measure their displacement over the celestial sphere with a level of accuracy that currently cannot be attained at any other wavelength. In particular, the accuracy achieved using carefully calibrated, phase-referenced observations with Very Long Baseline Interferometers such as NRAO's Very Long Baseline Array is better than 50 micro-arcseconds. This is sufficient to measure the trigonometric parallax and the proper motion of any radio-emitting young star within several hundred parsecs of the Sun with an acc…
We report 850~$μ$m dust polarization observations of a low-mass ($\sim$12 $M_{\odot}$) starless core in the $ρ$ Ophiuchus cloud, Ophiuchus C, made with the POL-2 instrument on the James Clerk Maxwell Telescope (JCMT) as part of the JCMT B-fields In STar-forming Region Observations (BISTRO) survey. We detect an ordered magnetic field projected on the plane of sky in the starless core. The magnetic field across the $\sim$0.1~pc core shows a predominant northeast-southwest orientation centering between $\sim$40$^\circ$ to $\sim$100$^\circ$, indicating that the field in the core is well aligned wi…
We use Smoothed Particle Hydrodynamics to explore the circumstances under which an isolated very-low-mass prestellar core can be formed by colliding turbulent flows and collapse to form a brown-dwarf. Our simulations suggest that the flows need not be very fast, but do need to be very strongly convergent, i.e. the gas must flow in at comparable speeds from all sides, which seems rather unlikely. We therefore revisit the object Oph-B11, which Andre, Ward-Thompson and Greaves (2012) have identified as a prestellar core with mass between $\sim 0.020\,\mathrm{M_\odot}$ and $\sim 0.030\,\mathrm{M_\…
We present 1.3 mm continuum ALMA long-baseline observations at 3-5 au resolution of 10 of the brightest discs from the Ophiuchus DIsc Survey Employing ALMA (ODISEA) project. We identify a total of 26 narrow rings and gaps distributed in 8 sources and 3 discs with small dust cavities (r $<$10 au). We find that two discs around embedded protostars lack the clear gaps and rings that are ubiquitous in more evolved sources with Class II SEDs. Our sample includes 5 objects with previously known large dust cavities (r $>$20 au). We find that the 1.3 mm radial profiles of these objects are in good agr…
We have used archival infrared images obtained with the Wide Field Camera 3 on board the Hubble Space Telescope to constrain the initial mass function of low-mass stars and brown dwarfs in the W3 star-forming region. The images cover 438 arcmin$^2$, which encompasses the entire complex, and were taken in the filters F110W, F139M, and F160W. We have estimated extinctions for individual sources in these data from their colors and have dereddened their photometry accordingly. By comparing an area of the images that contains the richest concentration of previously identified W3 members to an area …
SONYC, short for "Substellar Objects in Nearby Young Clusters", is a survey program to provide a census of the substellar population in nearby star forming regions. We have conducted deep optical and near-infrared photometry in five young regions (NGC1333, rho Ophiuchi, Chamaeleon-I, Upper Sco, and Lupus-3), combined with proper motions, and followed by extensive spectroscopic campaigns with Subaru and VLT, in which we have obtained more than 700 spectra of candidate low-mass objects. We have identified and characterized more than 60 new substellar objects, among them a handful of objects with…
The brown dwarf population in the canonical star forming region NGC2264 is so far poorly explored. We present a deep, multi-wavelength, multi-epoch survey of the star forming cluster NGC2264, aimed to identify young brown dwarf candidates in this region. Using criteria including optical/near-infrared colours, variability, Spitzer mid-infrared colour excess, extinction, and Gaia parallax and proper motion (in order of relevance), we select 902 faint red sources with indicators of youth. Within this sample we identify 429 brown dwarf candidates based on their infrared colours. The brown dwarf ca…
Very Long Baseline Interferometry (VLBI) at radio wavelengths can provide astrometry accurate to 10 micro-arcseconds or better (i.e. better than the target GAIA accuracy) without being limited by dust obscuration. This means that unlike GAIA, VLBI can be applied to star-forming regions independently of their internal and line-of-sight extinction. Low-mass young stellar objects (particularly T Tauri stars) are often non-thermal compact radio emitters, ideal for astrometric VLBI radio continuum experiments. Existing observations for nearby regions (e.g. Taurus, Ophiuchus, or Orion) demonstrate t…
We present the results of near-infrared imaging simulations of young star-forming regions in the Magellanic Clouds to be observed with the European Extremely Large Telescope (E-ELT). The simulated J,H,K-band images show that we should be able to obtain nearly complete samples of young brown dwarfs above the deuterium burning limit (M > 13 MJup) in low-mass star-forming regions in the Clouds. Moreover, very young giant planet-mass objects in the Clouds should be detectable with the E-ELT under favourable conditions.
We present combined interferometer and single dish telescope data of NH3 (J,K) = (1,1) and (2,2) emission towards the clustered star forming Ophiuchus B, C and F Cores at high spatial resolution (~1200 AU) using the Australia Telescope Compact Array, the Very Large Array, and the Green Bank Telescope. While the large scale features of the NH3 (1,1) integrated intensity appear similar to 850 micron continuum emission maps of the Cores, on 15" (1800 AU) scales we find significant discrepancies between the dense gas tracers in Oph B, but good correspondence in Oph C and F. Using the Clumpfind str…
The origin of the lowest mass free-floating objects -- brown dwarfs and planetary-mass objects -- is one of the major unsolved problems in star formation. Establishing a census of young substellar objects is a fundamental prerequisite for distinguishing between competing theoretical scenarios. Such a census allows us to probe the initial mass function (IMF), binary statistics, and properties of accretion disks. Our SONYC (Substellar Objects in Nearby Young Clusters) survey relies on extremely deep wide-field optical and near-infrared imaging, with follow-up spectroscopy, in combination with Sp…
Keck Observations in the INfrared of Taurus and $ρ$ Oph Exoplanets And Ultracool dwarfs (KOINTREAU) II: Two Young Bound Companions to Ophiuchus Stars
Institute for Astronomy at the University of Hawai‘i at Mānoa（夏威夷大学马诺阿分校天文研究所）；Department of Astronomy, California Institute of Technology（加州理工学院天文学系）；Jet Propulsion Laboratory, California Institute of Technology（加州理工学院喷气推进实验室）；Institute for Astronomy, University of Edinburgh（爱丁堡大学天文研究所）；Cahill Center for Astronomy and Astrophysics, California Institute of Technology（加州理工学院凯尔天文与天体物理中心）；P.E.S., Observatoire de la Côte d’Azur（蔚蓝海岸观测站）；California State University Northridge（北岭加州州立大学）
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-dime…
We present the results from an Atacama Large Millimeter/Submillimeter Array (ALMA) 1.3 mm continuum and $^{12}$CO ($J=2-1$) line survey spread over 10 square degrees in the Serpens star-forming region of 320 young stellar objects, 302 of which are likely members of Serpens (16 Class I, 35 Flat spectrum, 235 Class II, and 16 Class III). From the continuum data, we derive disk dust masses and show that they systematically decline from Class I to Flat spectrum to Class II sources. Grouped by stellar evolutionary state, the disk mass distributions are similar to other young ($<3$ Myr) regions, ind…
We present the results of a search for companions to young brown dwarfs in the Taurus and Chamaeleon I star forming regions (1/2-3 Myr). We have used WFPC2 on board HST to obtain F791W and F850LP images of 47 members of these regions that have spectral types of M6-L0 (0.01-0.1 Msun). An additional late-type member of Taurus, FU Tau (M7.25+M9.25), was also observed with adaptive optics at Keck Observatory. We have applied PSF subtraction to the primaries and have searched the resulting images for objects that have colors and magnitudes that are indicative of young low-mass objects. Through this…
We present results from a near-infrared (NIR) adaptive optics (AO) survey of pre-main-sequence stars in the Lupus Molecular Cloud with VLT/NACO to identify (sub)stellar companions down to $\sim$20 au separation and investigate the effects of multiplicity on circumstellar disc properties. We observe for the first time in the NIR with AO a total of 47 targets and complement our observations with archival data for another 58 objects previously observed with the same instrument. All 105 targets have millimetre ALMA data available, which provide constraints on disc masses and sizes. We identify a t…
Transition disks (TDs) are intermediate stage circumstellar disks characterized by an inner gap within the disk structure. To test whether these gaps may have been formed by closely orbiting, previously undetected stellar companions, we collected high-resolution optical spectra of 31 TD objects to search for spectroscopic binaries (SBs). Twenty-four of these objects are in Ophiuchus and seven are within the Coronet, Corona Australis, and Chameleon I star-forming regions. We measured radial velocities for multiple epochs, obtaining a median precision of 400 ms$^{-1}$. We identified double-lined…
We use $N$-body simulations to compare the evolution of spatial distributions of stars and brown dwarfs in young star-forming regions. We use three different diagnostics; the ratio of stars to brown dwarfs as a function of distance from the region's centre, $\mathcal{R}_{\rm SSR}$, the local surface density of stars compared to brown dwarfs, $Σ_{\rm LDR}$, and we compare the global spatial distributions using the $Λ_{\rm MSR}$ method. From a suite of twenty initially statistically identical simulations, 6/20 attain $\mathcal{R}_{\rm SSR} << 1$ $and$ $Σ_{\rm LDR} << 1$ $and$ $Λ_{\rm MSR} << 1$,…
