Publication Search Results

ID: 158754
Type: article
Authors: Maureira, María José; Arce, Héctor G.; Dunham, Michael M.; Mardones, Diego; Guzmán, Andrés E.; Pineda, Jaime E.; Bourke, Tyler L.
Abstract: We present ALMA 3 mm molecular line and continuum observations with a resolution of ˜3.5 arcsec towards five first hydrostatic core (FHSC) candidates (L1451-mm, Per-bolo 58, Per-bolo 45, L1448-IRS2E, and Cha-MMS1). Our goal is to characterize their envelopes and identify the most promising sources that could be bona fide FHSCs. We identify two candidates that are consistent with an extremely young evolutionary state (L1451-mm and Cha-MMS1), with L1451-mm being the most promising FHSC candidate. Although our envelope observations cannot rule out Cha-MMS1 as an FHSC yet, the properties of its CO outflow and SED published in recent studies are in better agreement with the predictions for a young protostar. For the remaining three sources, our observations favour a pre-stellar nature for Per-bolo 45 and rule out the rest as FHSC candidates. Per-bolo 58 is fully consistent with being a Class 0, while L1448 IRS2E shows no emission of high-density tracers (NH₂D and N₂H⁺) at the location of the previously identified compact continuum source, which is also undetected in our observations. Thus, we argue that there is no embedded source at the presumptive location of the FHSC candidate L1448 IRS2E. We propose instead that what was thought to be emission from the presumed L1448 IRS2E outflow corresponds to outflow emission from a nearby Class 0 system, deflected by the dense ambient material. We compare the properties of the FHSC candidates studied in this work and the literature, which shows that L1451-mm appears as possibly the youngest source with a confirmed outflow.

ID: 150899
Type: article
Authors: Andersen, Bridget C.; Stephens, Ian W.; Dunham, Michael M.; Pokhrel, Riwaj; Jørgensen, Jes K.; Frimann, Søren; Segura-Cox, Dominique; Myers, Philip C.; Bourke, Tyler L.; Tobin, John J.; Tychoniec, Łukasz
Abstract: In the standard picture for low-mass star formation, a dense molecular cloud undergoes gravitational collapse to form a protostellar system consisting of a new central star, a circumstellar disk, and a surrounding envelope of remaining material. The mass distribution of the system evolves as matter accretes from the large-scale envelope through the disk and onto the protostar. While this general picture is supported by simulations and indirect observational measurements, the specific timescales related to disk growth and envelope dissipation remain poorly constrained. In this paper we conduct a rigorous test of a method introduced by Jørgensen et al. to obtain mass measurements of disks and envelopes around embedded protostars with observations that do not resolve the disk (resolution of ˜1000 au). Using unresolved data from the recent Mass Assembly of Stellar Systems and their Evolution with the SMA (MASSES) survey, we derive disk and envelope mass estimates for 59 protostellar systems in the Perseus molecular cloud. We compare our results to independent disk mass measurements from the VLA Nascent Disk and Multiplicity survey and find a strong linear correlation, suggesting that accurate disk masses can be measured from unresolved observations. Then, leveraging the size of the MASSES sample, we find no significant trend in protostellar mass distribution as a function of age, as approximated from bolometric temperatures. These results may indicate that the disk mass of a protostar is set near the onset of the Class 0 protostellar stage and remains roughly constant throughout the Class I protostellar stage.

ID: 155442
Type: article
Authors: Caselli, Paola; Pineda, Jaime E.; Zhao, Bo; Walmsley, Malcolm C.; Keto, Eric; Tafalla, Mario; Chacón-Tanarro, Ana; Bourke, Tyler L.; Friesen, Rachel; Galli, Daniele; Padovani, Marco
Abstract: Stars like our Sun form in self-gravitating dense and cold structures within interstellar clouds that are referred to as pre-stellar cores. Although much is known about the physical structure of dense clouds just before and soon after the switch-on of a protostar, the central few thousand astronomical units (au) of pre-stellar cores are unexplored. It is within these central regions that stellar systems assemble and fragmentation may take place, with the consequent formation of binaries and multiple systems. We present Atacama Large Millimetre and submillimetre Array (ALMA) Band 6 observations (Atacama Compact Array and 12 m array) of the dust continuum emission of the 8 M _☉ pre-stellar core L1544, with an angular resolution of 2″ × 1.″6 (linear resolution 270 au × 216 au). Within the primary beam, a compact region of 0.1 M _☉, which we call a "kernel," has been unveiled. The kernel is elongated, with a central flat zone with radius R _ker ≃ 10″ (≃1400 au). The average number density within R _ker is ≃1 × 10⁶ cm^-3, with possible local density enhancements. The region within R _ker appears to have fragmented, but detailed analysis shows that similar substructure can be reproduced by synthetic interferometric observations of a smooth centrally concentrated dense core with a similar central flat zone. The presence of a smooth kernel within a dense core is in agreement with non-ideal magnetohydro-dynamical simulations of a contracting cloud core with a peak number density of 1 × 10⁷ cm^-3. Dense cores with lower central densities are completely filtered out when simulated 12 m array observations are carried out. These observations demonstrate that the kernel of dynamically evolved dense cores can be investigated at high angular resolution with ALMA.

ID: 154516
Type: article
Authors: Stephens, Ian W.; Bourke, Tyler L.; Dunham, Michael M.; Myers, Philip C.; Pokhrel, Riwaj; Tobin, John J.; Arce, Héctor G.; Sadavoy, Sarah I.; Vorobyov, Eduard I.; Pineda, Jaime E.; Offner, Stella S. R.; Lee, Katherine I.; Kristensen, Lars E.; Jørgensen, Jes K.; Gurwell, Mark A.; Goodman, Alyssa A.
Abstract: We present and release the full data set for the Mass Assembly of Stellar Systems and their Evolution with the SMA (MASSES) survey. This survey used the Submillimeter Array (SMA) to image the 74 known protostars within the Perseus molecular cloud. The SMA was used in two array configurations to capture outflows for scales >30″ (>9000 au) and to probe scales down to ∼1″ (∼300 au). The protostars were observed with the 1.3 mm and 850 μm receivers simultaneously to detect continuum at both wavelengths and molecular line emission from CO(2─1), ¹³CO(2─1), C¹⁸O(2─1), N₂D⁺(3─2), CO(3─2), HCO⁺(4─3), and H¹³CO⁺(4─3). Some of the observations also used the SMA's recently upgraded correlator, SWARM, whose broader bandwidth allowed for several more spectral lines to be observed (e.g., SO, H₂CO, DCO⁺, DCN, CS, CN). Of the main continuum and spectral tracers observed, 84% of the images and cubes had emission detected. The median C¹⁸O(2─1) line width is ∼1.0 km s⁻¹, which is slightly higher than those measured with single-dish telescopes at scales of 3000─20,000 au. Of the 74 targets, six are suggested to be first hydrostatic core candidates, and we suggest that L1451-mm is the best candidate. We question a previous continuum detection toward L1448 IRS2E. In the SVS 13 system, SVS 13A certainly appears to be the most evolved source, while SVS 13C appears to be hotter and more evolved than SVS 13B. The MASSES survey is the largest publicly available interferometric continuum and spectral line protostellar survey to date, and is largely unbiased as it only targets protostars in Perseus. All visibility (uv) data and imaged data are publicly available at https://dataverse.harvard.edu/dataverse/full_MASSES/.

ID: 145756
Type: article
Authors: Pokhrel, Riwaj; Myers, Philip C.; Dunham, Michael M.; Stephens, Ian W.; Sadavoy, Sarah I.; Zhang, Qizhou; Bourke, Tyler L.; Tobin, John J.; Lee, Katherine I.; Gutermuth, Robert A.; Offner, Stella S. R.
Abstract: We present a study of hierarchical structure in the Perseus molecular cloud, from the scale of the entire cloud (≳ 10 pc) to smaller clumps (~1 pc), cores (~0.05--0.1 pc), envelopes (~300--3000 au), and protostellar objects (~15 au). We use new observations from the Submillimeter Array (SMA) large project ``Mass Assembly of Stellar Systems and their Evolution with the SMA (MASSES)'' to probe the envelopes, and recent single-dish and interferometric observations from the literature for the remaining scales. This is the first study to analyze hierarchical structure over five scales in the same cloud complex. We compare the number of fragments with the number of Jeans masses in each scale to calculate the Jeans efficiency, or the ratio of observed to expected number of fragments. The velocity dispersion is assumed to arise either from purely thermal motions or from combined thermal and non-thermal motions inferred from observed spectral line widths. For each scale, thermal Jeans fragmentation predicts more fragments than observed, corresponding to inefficient thermal Jeans fragmentation. For the smallest scale, thermal plus non-thermal Jeans fragmentation also predicts too many protostellar objects. However, at each of the larger scales thermal plus non-thermal Jeans fragmentation predicts fewer than one fragment, corresponding to no fragmentation into envelopes, cores, and clumps. Over all scales, the results are inconsistent with complete Jeans fragmentation based on either thermal or thermal plus non-thermal motions. They are more nearly consistent with inefficient thermal Jeans fragmentation, where the thermal Jeans efficiency increases from the largest to the smallest scale.

ID: 145763
Type: article
Authors: Sadavoy, Sarah I.; Keto, Eric; Bourke, Tyler L.; Dunham, Michael M.; Myers, Philip C.; Stephens, Ian W.; di Francesco, James; Webb, Kristi; Stutz, Amelia M.; Launhardt, Ralf; Tobin, John J.
Abstract: We present intensity-corrected Herschel maps at 100, 160, 250, 350, and 500 mum for 56 isolated low-mass clouds. We determine the zero-point corrections for Herschel Photodetector Array Camera and Spectrometer (PACS) and Spectral Photometric Imaging Receiver (SPIRE) maps from the Herschel Science Archive (HSA) using Planck data. Since these HSA maps are small, we cannot correct them using typical methods. Here we introduce a technique to measure the zero-point corrections for small Herschel maps. We use radial profiles to identify offsets between the observed HSA intensities and the expected intensities from Planck. Most clouds have reliable offset measurements with this technique. In addition, we find that roughly half of the clouds have underestimated HSA-SPIRE intensities in their outer envelopes relative to Planck, even though the HSA-SPIRE maps were previously zero-point corrected. Using our technique, we produce corrected Herschel intensity maps for all 56 clouds and determine their line-of-sight average dust temperatures and optical depths from modified blackbody fits. The clouds have typical temperatures of ~14--20 K and optical depths of ~10^-5--10^-3. Across the whole sample, we find an anticorrelation between temperature and optical depth. We also find lower temperatures than what was measured in previous Herschel studies, which subtracted out a background level from their intensity maps to circumvent the zero-point correction. Accurate Herschel observations of clouds are key to obtaining accurate density and temperature profiles. To make such future analyses possible, intensity-corrected maps for all 56 clouds are publicly available in the electronic version. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.

ID: 148980
Type: article
Authors: Stephens, Ian W.; Dunham, Michael M.; Myers, Philip C.; Pokhrel, Riwaj; Bourke, Tyler L.; Vorobyov, Eduard I.; Tobin, John J.; Sadavoy, Sarah I.; Pineda, Jaime E.; Offner, Stella S. R.; Lee, Katherine I.; Kristensen, Lars E.; Jørgensen, Jes K.; Goodman, Alyssa A.; Arce, Héctor G.; Gurwell, Mark
Abstract: We present the Mass Assembly of Stellar Systems and their Evolution with the SMA (MASSES) survey, which uses the Submillimeter Array (SMA) interferometer to map the continuum and molecular lines for all 74 known Class 0/I protostellar systems in the Perseus molecular cloud. The primary goal of the survey is to observe an unbiased sample of young protostars in a single molecular cloud so that we can characterize the evolution of protostars. This paper releases the MASSES 1.3 mm data from the subcompact configuration (˜4" or ˜1000 au resolution), which is the SMA's most compact array configuration. We release both uv visibility data and imaged data for the spectral lines CO(2-1), ¹³CO(2-1), C¹⁸O(2-1), and N₂D⁺(3-2), as well as for the 1.3 mm continuum. We identify the tracers that are detected toward each source. We also show example images of continuum and CO(2-1) outflows, analyze C¹⁸O(2-1) spectra, and present data from the SVS 13 star-forming region. The calculated envelope masses from the continuum show a decreasing trend with bolometric temperature (a proxy for age). Typical C¹⁸O(2-1) line widths are 1.45 km s^-1, which is higher than the C¹⁸O line widths detected toward Perseus filaments and cores. We find that N₂D⁺(3-2) is significantly more likely to be detected toward younger protostars. We show that the protostars in SVS 13 are contained within filamentary structures as traced by C¹⁸O(2-1) and N₂D⁺(3-2). We also present the locations of SVS 13A's high-velocity (absolute line-of-sight velocities >150 km s^-1) red and blue outflow components. Data can be downloaded from https://dataverse.harvard.edu/dataverse/MASSES.

ID: 147076
Type: article
Authors: Tobin, John J.; Bos, Steven P.; Dunham, Michael M.; Bourke, Tyler L.; van der Marel, Nienke
Abstract: We present a characterization of the protostar embedded within the BHR7 dark cloud, based on both photometric measurements from the near-infrared to millimeter and interferometric continuum and molecular line observations at millimeter wavelengths. We find that this protostar is a Class 0 system, the youngest class of protostars, measuring its bolometric temperature to be 50.5 K, with a bolometric luminosity of 9.3 L _&sun;. The near-infrared and Spitzer imaging show a prominent dark lane from dust extinction separating clear bipolar outflow cavities. Observations of ¹³CO (J=2\to 1), C¹⁸O (J=2\to 1), and other molecular lines with the Submillimeter Array (SMA) exhibit a clear rotation signature on scales O (J=2\to 1), and other molecular lines with the Submillimeter Array (SMA) exhibit a clear rotation signature on scales ^-1 profile, implying that angular momentum is being conserved. Observations of the 1.3 mm dust continuum with the SMA reveal a resolved continuum source, extended in the direction of the dark lane, orthogonal to the outflow. The deconvolved size of the continuum indicates a radius of ~100 au for the continuum source at the assumed distance of 400 pc. The visibility amplitude profile of the continuum emission cannot be reproduced by an envelope alone and needs a compact component. Thus, we posit that the resolved continuum source could be tracing a Keplerian disk in this very young system. If we assume that the continuum radius traces a Keplerian disk (R ~ 120 au) the observed rotation profile is consistent with a protostar mass of 1.0 M _&sun;.

ID: 144740
Type: article
Authors: Fayolle, Edith C.; Öberg, Karin I.; Jørgensen, Jes K.; Altwegg, Kathrin; Calcutt, Hannah; Müller, Holger S. P.; Rubin, Martin; van der Wiel, Matthijs H. D.; Bjerkeli, Per; Bourke, Tyler L.; Coutens, Audrey; van Dishoeck, Ewine F.; Drozdovskaya, Maria N.; Garrod, Robin T.; Ligterink, Niels F. W.; Persson, Magnus V.; Wampfler, Susanne F.; Rosina Team
Abstract: Organohalogens, a class of molecules that contain at least one halogen atom bonded to carbon, are abundant on the Earth where they are mainly produced through industrial and biological processes¹. Consequently, they have been proposed as biomarkers in the search for life on exoplanets². Simple halogen hydrides have been detected in interstellar sources and in comets, but the presence and possible incorporation of more complex halogen-containing molecules such as organohalogens into planet-forming regions is uncertain^3,4. Here we report the interstellar detection of two isotopologues of the organohalogen CH₃Cl and put some constraints on CH₃F in the gas surrounding the low-mass protostar IRAS 16293-2422, using the Atacama Large Millimeter/submillimeter Array (ALMA). We also find CH₃Cl in the coma of comet 67P/Churyumov-Gerasimenko (67P/C-G) by using the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) instrument. The detections reveal an efficient pre-planetary formation pathway of organohalogens. Cometary impacts may deliver these species to young planets and should thus be included as a potential abiotical production source when interpreting future organohalogen detections in atmospheres of rocky planets.

ID: 144730
Type: article
Authors: Stephens, Ian W.; Dunham, Michael M.; Myers, Philip C.; Pokhrel, Riwaj; Sadavoy, Sarah I.; Vorobyov, Eduard I.; Tobin, John J.; Pineda, Jaime E.; Offner, Stella S. R.; Lee, Katherine I.; Kristensen, Lars E.; Jørgensen, Jes K.; Goodman, Alyssa A.; Bourke, Tyler L.; Arce, Héctor G.; Plunkett, Adele L.
Abstract: We present new Submillimeter Array (SMA) observations of CO(2-1) outflows toward young, embedded protostars in the Perseus molecular cloud as part of the Mass Assembly of Stellar Systems and their Evolution with the SMA (MASSES) survey. For 57 Perseus protostars, we characterize the orientation of the outflow angles and compare them with the orientation of the local filaments as derived from Herschel observations. We find that the relative angles between outflows and filaments are inconsistent with purely parallel or purely perpendicular distributions. Instead, the observed distribution of outflow-filament angles are more consistent with either randomly aligned angles or a mix of projected parallel and perpendicular angles. A mix of parallel and perpendicular angles requires perpendicular alignment to be more common by a factor of ~3. Our results show that the observed distributions probably hold regardless of the protostar's multiplicity, age, or the host core's opacity. These observations indicate that the angular momentum axis of a protostar may be independent of the large-scale structure. We discuss the significance of independent protostellar rotation axes in the general picture of filament-based star formation.

ID: 141962
Type: article
Authors: Keown, Jared; Schnee, Scott; Bourke, Tyler L.; di Francesco, James; Friesen, Rachel; Caselli, Paola; Myers, Philip C.; Williger, Gerard; Tafalla, Mario
Abstract: Although surveys of infall motions in dense cores have been carried out for years, few surveys have focused on mapping infall across cores using multiple spectral-line observations. To fill this gap, we present IRAM 30 m telescope maps of N₂H⁺(1-0), DCO⁺(2-1), DCO⁺(3-2), and HCO⁺(3-2) emission toward two prestellar cores (L492 and L694-2) and one protostellar core (L1521F). We find that the measured infall velocity varies with position across each core and choice of molecular line, likely as a result of radial variations in core chemistry and dynamics. Line-of-sight infall speeds estimated from DCO⁺(2-1) line profiles can decrease by 40-50 m s^-1 when observing at a radial offset ≥slant 0.04 pc from the core's dust continuum emission peak. Median infall speeds calculated from all observed positions across a core can also vary by as much as 65 m s^-1, depending on the transition. These results show that while single-pointing, single-transition surveys of core infall velocities may be good indicators of whether a core is either contracting or expanding, the magnitude of the velocities they measure are significantly impacted by the choice of molecular line, proximity to the core center, and core evolutionary state.

ID: 139317
Type: article
Authors: Lee, Katherine I.; Dunham, Michael M.; Myers, Philip C.; Arce, Héctor G.; Bourke, Tyler L.; Goodman, Alyssa A.; Jørgensen, Jes K.; Kristensen, Lars E.; Offner, Stella S. R.; Pineda, Jaime E.; Tobin, John J.; Vorobyov, Eduard I.
Abstract: We investigate the alignment between outflow axes in nine of the youngest binary/multiple systems in the Perseus Molecular Cloud. These systems have typical member spacing larger than 1000 au. For outflow identification, we use ¹²CO(2-1) and ¹²CO(3-2) data from a large survey with the Submillimeter Array: Mass Assembly of Stellar Systems and their Evolution with the SMA. The distribution of outflow orientations in the binary pairs is consistent with random or preferentially anti-aligned distributions, demonstrating that these outflows are misaligned. This result suggests that these systems are possibly formed in environments where the distribution of angular momentum is complex and disordered, and these systems do not come from the same co-rotating structures or from an initial cloud with aligned vectors of angular momentum.

ID: 140755
Type: article
Authors: Suresh, Akshaya; Dunham, Michael M.; Arce, Héctor G.; Evans, Neal J., II; Bourke, Tyler L.; Merello, Manuel; Wu, Jingwen
Abstract: We present a catalog of low-mass dense cores observed with the SHARC-II instrument at 350 μm. Our observations have an effective angular resolution of 10″, approximately 2.5 times higher than observations at the same wavelength obtained with the Herschel Space Observatory, albeit with lower sensitivity, especially to extended emission. The catalog includes 81 maps covering a total of 164 detected sources. For each detected source, we tabulate basic source properties including position, peak intensity, flux density in fixed apertures, and radius. We examine the uncertainties in the pointing model applied to all SHARC-II data and conservatively find that the model corrections are good to within ˜3″, approximately 1/3 of the SHARC-II beam. We examine the differences between two array scan modes and find that the instrument calibration, beam size, and beam shape are similar between the two modes. We also show that the same flux densities are measured when sources are observed in the two different modes, indicating that there are no systematic effects introduced into our catalog by utilizing two different scan patterns during the course of taking observations. We find a detection rate of 95% for protostellar cores but only 45% for starless cores, and demonstrate the existence of a SHARC-II detection bias against all but the most massive and compact starless cores. Finally, we discuss the improvements in protostellar classification enabled by these 350 μm observations.

ID: 134227
Type: article
Authors: Broekhoven-Fiene, Hannah; Matthews, Brenda C.; Harvey, Paul M.; Gutermuth, Robert A.; Huard, Tracy L.; Tothill, Nicholas F. H.; Nutter, David; Bourke, Tyler L.; di Francesco, James; Jørgensen, Jes K.; Allen, Lori E.; Chapman, Nicholas L.; Cieza, Lucas A.; Dunham, Michael M.; Merín, Bruno; Miller, Jennifer F.; Terebey, Susan; Peterson, Dawn E.; Stapelfeldt, Karl R.
Abstract: Not Available

ID: 138592
Type: article
Authors: Lee, Katherine I.; Dunham, Michael M.; Myers, Philip C.; Tobin, John J.; Kristensen, Lars E.; Pineda, Jaime E.; Vorobyov, Eduard I.; Offner, Stella S. R.; Arce, Héctor G.; Li, Zhi-Yun; Bourke, Tyler L.; Jørgensen, Jes K.; Goodman, Alyssa A.; Sadavoy, Sarah I.; Chandler, Claire J.; Harris, Robert J.; Kratter, Kaitlin; Looney, Leslie W.; Melis, Carl; Perez, Laura M.; Segura-Cox, Dominique
Abstract: We present continuum and molecular line observations at 230 and 345 GHz from the Submillimeter Array (SMA) toward three protostars in the Perseus L1448N region. The data are from the large project “Mass Assembly of Stellar Systems and their Evolution with the SMA.” Three dust continuum sources, Source B, Source NW, and Source A, are detected at both frequencies. These sources have corresponding emission peaks in C¹⁸O (J=2\to 1), ¹³CO (J=2\to 1), and HCO⁺ (J=4\to 3), and have offsets with N₂D⁺ (J=3\to 2) peaks. High angular resolution data from a complementary continuum survey with the Karl G. Jansky Very Large Array show that Source B is associated with three 8 mm continuum objects, Source NW with two, and Source A remains single. These results suggest that multiplicity in L1448N exists at different spatial scales from a few thousand AU to (J=3\to 2) peaks. High angular resolution data from a complementary continuum survey with the Karl G. Jansky Very Large Array show that Source B is associated with three 8 mm continuum objects, Source NW with two, and Source A remains single. These results suggest that multiplicity in L1448N exists at different spatial scales from a few thousand AU to ¹⁸O emission are found to be perpendicular to within 20° of the outflow directions as revealed by ¹²CO (J=2\to 1). We have observed that Sources B and NW with multiplicity have higher densities than Source A without multiplicity. This suggests that thermal Jeans fragmentation can be relevant in the fragmentation process. However, we have not observed a difference in the ratio between rotational and gravitational energy between sources with and without multiplicity. We also have not observed a trend between non-thermal velocity dispersions and the level of fragmentation. Our study has provided the first direct and comprehensive comparison between multiplicity and core properties in low-mass protostars, although based on small number statistics.

ID: 135159
Type: article
Authors: Pineda, Jaime E.; Offner, Stella S. R.; Parker, Richard J.; Arce, Héctor G.; Goodman, Alyssa A.; Caselli, Paola; Fuller, Gary A.; Bourke, Tyler L.; Corder, Stuartt A.
Abstract: The initial multiplicity of stellar systems is highly uncertain. A number of mechanisms have been proposed to explain the origin of binary and multiple star systems, including core fragmentation, disk fragmentation and stellar capture. Observations show that protostellar and pre-main-sequence multiplicity is higher than the multiplicity found in field stars, which suggests that dynamical interactions occur early, splitting up multiple systems and modifying the initial stellar separations. Without direct, high-resolution observations of forming systems, however, it is difficult to determine the true initial multiplicity and the dominant binary formation mechanism. Here we report observations of a wide-separation (greater than 1,000 astronomical units) quadruple system composed of a young protostar and three gravitationally bound dense gas condensations. These condensations are the result of fragmentation of dense gas filaments, and each condensation is expected to form a star on a timescale of 40,000 years. We determine that the closest pair will form a bound binary, while the quadruple stellar system itself is bound but unstable on timescales of 500,000 years (comparable to the lifetime of the embedded protostellar phase). These observations suggest that filament fragmentation on length scales of about 5,000 astronomical units offers a viable pathway to the formation of multiple systems.

ID: 136595
Type: article
Authors: Tobin, John J.; Looney, Leslie W.; Wilner, David J.; Kwon, Woojin; Chandler, Claire J.; Bourke, Tyler L.; Loinard, Laurent; Chiang, Hsin-Fang; Schnee, Scott; Chen, Xuepeng
Abstract: We present a 1.3 mm dust continuum survey toward nine Class 0 protostars and two Class I protostars in the Perseus molecular cloud, using CARMA with a resolution of ~0.?3 (70 AU). This sample approximately doubles the number of Class 0 protostars observed with spatial resolutions 100 AU around two sources (L1448 IRS2 and Per-emb-14), and these sources may be strong disk candidates. Marginally resolved structures within 30° of perpendicular to the outflow are found toward three protostars (L1448 IRS3C, IRAS 03282+3035, L1448C) and are considered disk candidates. Two others (L1448 IRS3B, IRAS 03292+3039) have complex resolved structures, possibly indicative of massive, fragmenting inner envelopes or disks; L1448 IRS3B also has evidence for a companion separated by 0.?9 (~210 AU). The candidate first hydrostatic core L1451-MMS is marginally resolved on 1? scales and the Class 0 protostar IC 348-MMS and does not have strong indications of resolved structure at any scale. The strong disk candidate sources were followed up with C¹⁸O (J=2\to 1) observations; we detect velocity gradients that are consistent with the expected rotation axis, but without enough sensitivity to determine if it is Keplerian. We compare the observed visibility amplitudes to radiative transfer models of protostellar envelopes and disks. The visibility amplitude ratios show that a compact component (possibly a disk) is necessary for five of nine Class 0 sources. An envelope-only scenario cannot be ruled out for the other four Class 0 sources. We conclude that there is evidence for the formation of large disks in the Class 0 phase, but Class 0 disks likely have a range of radii and masses that depend on the initial conditions of their parent cores.

ID: 123036
Type: article
Authors: Broekhoven-Fiene, Hannah; Matthews, Brenda C.; Harvey, Paul M.; Gutermuth, Robert A.; Huard, Tracy L.; Tothill, Nicholas F. H.; Nutter, David; Bourke, Tyler L.; DiFrancesco, James; Jørgensen, Jes K.; Allen, Lori E.; Chapman, Nicholas L.; Dunham, Michael M.; Merín, Bruno; Miller, Jennifer F.; Terebey, Susan; Peterson, Dawn E.; Stapelfeldt, Karl R.
Abstract: We present observations of the Auriga-California Molecular Cloud (AMC) at 3.6, 4.5, 5.8, 8.0, 24, 70, and 160 μm observed with the IRAC and MIPS detectors as part of the Spitzer Gould Belt Legacy Survey. The total mapped areas are 2.5 deg² with IRAC and 10.47 deg² with MIPS. This giant molecular cloud is one of two in the nearby Gould Belt of star-forming regions, the other being the Orion A Molecular Cloud (OMC). We compare source counts, colors, and magnitudes in our observed region to a subset of the SWIRE data that was processed through our pipeline. Using color-magnitude and color-color diagrams, we find evidence for a substantial population of 166 young stellar objects (YSOs) in the cloud, many of which were previously unknown. Most of this population is concentrated around the LkHα 101 cluster and the filament extending from it. We present a quantitative description of the degree of clustering and discuss the relative fraction of YSOs in earlier (Class I and F) and later (Class II) classes compared to other clouds. We perform simple SED modeling of the YSOs with disks to compare the mid-IR properties to disks in other clouds and identify 14 classical transition disk candidates. Although the AMC is similar in mass, size, and distance to the OMC, it is forming about 15-20 times fewer stars.

ID: 127637
Type: article
Authors: Favre, Cécile; Jørgensen, Jes K.; Field, David; Brinch, Christian; Bisschop, Suzanne E.; Bourke, Tyler L.; Hogerheijde, Michiel R.; Frieswijk, Wilfred W. F.
Abstract: A fundamental question about the early evolution of low-mass protostars is when circumstellar disks may form. High angular resolution observations of molecular transitions in the (sub)millimeter wavelength windows make it possible to investigate the kinematics of the gas around newly formed stars, for example, to identify the presence of rotation and infall. IRAS 16293–2422 was observed with the extended Submillimeter Array (eSMA) resulting in subarcsecond resolution (0.''46 × 0.''29, i.e., ~55 × 35 AU) images of compact emission from the C¹⁷O (3-2) and C³⁴S (7-6) transitions at 337 GHz (0.89 mm). To recover the more extended emission we have combined the eSMA data with SMA observations of the same molecules. The emission of C¹⁷O (3-2) and C³⁴S (7-6) both show a velocity gradient oriented along a northeast-southwest direction with respect to the continuum marking the location of one of the components of the binary, IRAS 16293A. Our combined eSMA and SMA observations show that the velocity field on the 50-400 AU scales is consistent with a rotating structure. It cannot be explained by simple Keplerian rotation around a single point mass but rather needs to take into account the enclosed envelope mass at the radii where the observed lines are excited. We suggest that IRAS 16293–2422 could be among the best candidates to observe a pseudo-disk with future high angular resolution observations.