Publication Search Results

ID: 159349
Type: article
Authors: Reynolds, Nickalas K.; Tobin, John J.; Sheehan, Patrick; Sadavoy, Sarah I.; Kratter, Kaitlin M.; Li, Zhi-Yun; Chandler, Claire J.; Segura-Cox, Dominique; Looney, Leslie W.; Dunham, Michael M.
Abstract: We present new Atacama Large Millimeter/submillimeter Array observations toward a compact (∼230 au separation) triple protostar system, L1448 IRS3B, at 879 μm with 0"11 × 0"05 resolution. Spiral arm structure within the circum-multiple disk is well resolved in dust continuum toward IRS3B, and we detect the known wide (∼2300 au) companion, IRS3A, also resolving possible spiral substructure. Using dense gas tracers, C¹⁷O (J = 3 $\to $ 2), H¹³CO⁺ (J = 4 $\to $ 3), and H¹³CN (J = 4 $\to $ 3), we resolve the Keplerian rotation for both the circum-triple disk in IRS3B and the disk around IRS3A. Furthermore, we use the molecular line kinematic data and radiative transfer modeling of the molecular line emission to confirm that the disks are in Keplerian rotation with fitted masses of ${1.19}_{-0.07}^{+0.13}$ M_⊙ for IRS3B-ab and ${1.51}_{-0.07}^{+0.06}$ M_⊙ for IRS3A and place an upper limit on the central protostar mass for the tertiary IRS3B-c of 0.2 M_⊙. We measure the mass of the fragmenting disk of IRS3B to be ∼0.29 M_⊙ from the dust continuum emission of the circum-multiple disk and estimate the mass of the clump surrounding IRS3B-c to be 0.07 M_⊙. We also find that the disk around IRS3A has a mass of ∼0.04 M_⊙. By analyzing the Toomre Q parameter, we find the IRS3A circumstellar disk is gravitationally stable (Q > 5), while the IRS3B disk is consistent with a gravitationally unstable disk (Q < 1) between the radii ∼200-500 au. This coincides with the location of the spiral arms and the tertiary companion IRS3B-c, supporting the hypothesis that IRS3B-c was formed in situ via fragmentation of a gravitationally unstable disk.

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: 157803
Type: article
Authors: Pokhrel, Riwaj; Gutermuth, Robert A.; Betti, Sarah K.; Offner, Stella S. R.; Myers, Philip C.; Megeath, S. Thomas; Sokol, Alyssa D.; Ali, Babar; Allen, Lori; Allen, Thomas S.; Dunham, Michael M.; Fischer, William J.; Henning, Thomas; Heyer, Mark; Hora, Joseph L.; Pipher, Judith L.; Tobin, John J.; Wolk, Scott J.
Abstract: We explore the relation between the stellar mass surface density and the mass surface density of molecular hydrogen gas in 12 nearby molecular clouds that are located at <1.5 kpc distance. The sample clouds span an order-of-magnitude range in mass, size, and star formation rates. We use thermal dust emission from Herschel maps to probe the gas surface density and the young stellar objects from the most recent Spitzer Extended Solar Neighborhood Archive catalog to probe the stellar surface density. Using a star-sampled nearest neighbor technique to probe the star-gas surface density correlations at the scale of a few parsecs, we find that the stellar mass surface density varies as a power law of the gas mass surface density, with a power-law index of ∼2 in all the clouds. The consistent power-law index implies that star formation efficiency is directly correlated with gas column density, and no gas column density threshold for star formation is observed. We compare the observed correlations with the predictions from an analytical model of thermal fragmentation and with the synthetic observations of a recent hydrodynamic simulation of a turbulent star-forming molecular cloud. We find that the observed correlations are consistent for some clouds with the thermal fragmentation model and can be reproduced using the hydrodynamic simulations.

ID: 156217
Type: article
Authors: Tobin, John J.; Sheehan, Patrick D.; Megeath, S. Thomas; Díaz-Rodríguez, Ana Karla; Offner, Stella S. R.; Murillo, Nadia M.; van 't Hoff, Merel L. R.; van Dishoeck, Ewine F.; Osorio, Mayra; Anglada, Guillem; Furlan, Elise; Stutz, Amelia M.; Reynolds, Nickalas; Karnath, Nicole; Fischer, William J.; Persson, Magnus; Looney, Leslie W.; Li, Zhi-Yun; Stephens, Ian; Chandler, Claire J.; Cox, Erin; Dunham, Michael M.; Tychoniec, Łukasz; Kama, Mihkel; Kratter, Kaitlin; Kounkel, Marina; Mazur, Brian; Maud, Luke; Patel, Lisa; Perez, Laura; Sadavoy, Sarah I.; Segura-Cox, Dominique; Sharma, Rajeeb; Stephenson, Brian; Watson, Dan M.; Wyrowski, Friedrich
Abstract: We have conducted a survey of 328 protostars in the Orion molecular clouds with the Atacama Large Millimeter/submillimeter Array at 0.87 mm at a resolution of ∼0"1 (40 au), including observations with the Very Large Array at 9 mm toward 148 protostars at a resolution of ∼0"08 (32 au). This is the largest multiwavelength survey of protostars at this resolution by an order of magnitude. We use the dust continuum emission at 0.87 and 9 mm to measure the dust disk radii and masses toward the Class 0, Class I, and flat-spectrum protostars, characterizing the evolution of these disk properties in the protostellar phase. The mean dust disk radii for the Class 0, Class I, and flat-spectrum protostars are ${44.9}_{-3.4}^{+5.8}$ , ${37.0}_{-3.0}^{+4.9}$ , and ${28.5}_{-2.3}^{+3.7}$ au, respectively, and the mean protostellar dust disk masses are 25.9 ${}_{-4.0}^{+7.7}$ , ${14.9}_{-2.2}^{+3.8}$ , ${11.6}_{-1.9}^{+3.5}$ ${M}_{\oplus }$ , respectively. The decrease in dust disk masses is expected from disk evolution and accretion, but the decrease in disk radii may point to the initial conditions of star formation not leading to the systematic growth of disk radii or that radial drift is keeping the dust disk sizes small. At least 146 protostellar disks (35% of 379 detected 0.87 mm continuum sources plus 42 nondetections) have disk radii greater than 50 au in our sample. These properties are not found to vary significantly between different regions within Orion. The protostellar dust disk mass distributions are systematically larger than those of Class II disks by a factor of >4, providing evidence that the cores of giant planets may need to at least begin their formation during the protostellar phase.

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: 150506
Type: article
Authors: Li, Juan; Myers, Philip C.; Kirk, Helen; Gutermuth, Robert A.; Dunham, Michael M.; Pokhrel, Riwaj
Abstract: We analyze high-quality stellar catalogs for 24 young and nearby (within 1 kpc) embedded clusters and present a catalog of 32 groups which have a high concentration of protostars. The median effective radius of these groups is 0.17 pc. The median protostellar and pre-main-sequence star surface densities are 46 M _⊙ pc^‑2 and 11 M _⊙ pc^‑2, respectively. We estimate the age of these groups using a model of constant birthrate and random accretion stopping and find a median value of 0.25 Myr. Some groups in Aquila, Serpens, Corona Australia, and Ophichus L1688 show high protostellar surface density and high molecular gas surface density, and seem to be undergoing vigorous star formation. These groups provide an excellent opportunity to study the initial conditions of clustered star formation. Comparisons of protostellar and pre-main-sequence stellar surface densities reveal continuous low-mass star formation of these groups over several Myr in some clouds. For groups with typical protostellar separations of less than 0.4 pc, we find that these separations agree well with the thermal Jeans fragmentation scale. On the other hand, for groups with typical protostellar separations larger than 0.4 pc, these separations are always larger than the associated Jeans length.

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: 154585
Type: article
Authors: Tobin, John J.; Megeath, S. Thomas; van't Hoff, Merel; Díaz-Rodríguez, Ana Karla; Reynolds, Nickalas; Osorio, Mayra; Anglada, Guillem; Furlan, Elise; Karnath, Nicole; Offner, Stella S. R.; Sheehan, Patrick D.; Sadavoy, Sarah I.; Stutz, Amelia M.; Fischer, William J.; Kama, Mihkel; Persson, Magnus; di Francesco, James; Looney, Leslie W.; Watson, Dan M.; Li, Zhi-Yun; Stephens, Ian; Chandler, Claire J.; Cox, Erin; Dunham, Michael M.; Kratter, Kaitlin; Kounkel, Marina; Mazur, Brian; Murillo, Nadia M.; Patel, Lisa; Perez, Laura; Segura-Cox, Dominique; Sharma, Rajeeb; Tychoniec, Łukasz; Wyrowski, Friedrich
Abstract: We present Atacama Large Millimeter/submillimeter Array (0.87 mm) and Very Large Array (9 mm) observations toward OMC-2 FIR4 and OMC-2 FIR3 within the Orion integral-shaped filament, thought to be two of the nearest regions of intermediate-mass star formation. We characterize the continuum sources within these regions on ∼40 au (0.″1) scales and associated molecular line emission at a factor of ∼30 better resolution than previous observations at similar wavelengths. We identify six compact continuum sources within OMC-2 FIR4, four in OMC-2 FIR3, and one additional source just outside OMC-2 FIR4. This continuum emission is tracing the inner envelope and/or disk emission on less than 100 au scales. HOPS-108 is the only protostar in OMC-2 FIR4 that exhibits emission from high-excitation transitions of complex organic molecules (e.g., methanol and other lines) coincident with the continuum emission. HOPS-370 in OMC-2 FIR3, with L ∼ 360 L _☉, also exhibits emission from high-excitation methanol and other lines. The methanol emission toward these two protostars is indicative of temperatures high enough to thermally evaporate it from icy dust grains; overall, these protostars have characteristics similar to hot corinos. We do not identify a clear outflow from HOPS-108 in ¹²CO, but we find evidence of interaction between the outflow/jet from HOPS-370 and the OMC-2 FIR4 region. A multitude of observational constraints indicate that HOPS-108 is likely a low- to intermediate-mass protostar in its main mass accretion phase and is the most luminous protostar in OMC-2 FIR4. The high-resolution data presented here are essential for disentangling the embedded protostars from their surrounding dusty environments and characterizing them.

ID: 149162
Type: article
Authors: Law, Charles J.; Zhang, Qizhou; Ricci, Luca; Petitpas, Glen; Jiménez-Donaire, Maria J.; Ueda, Junko; Lu, Xing; Dunham, Michael M.
Abstract: We present moderate (∼5″) and high angular resolution (∼1″) observations of ¹²CO (J = 2 ‑ 1) emission toward the nearby interacting galaxy NGC 3627 taken with the Submillimeter Array (SMA). These SMA mosaic maps of NGC 3627 reveal a prominent nuclear peak, inter-arm regions, and diffuse, extended emission in the spiral arms. A velocity gradient of ∼400–450 km s^‑1 is seen across the entire galaxy with velocity dispersions ranging from ≲80 km s^‑1 toward the nuclear region to ≲15 km s^‑1 in the spiral arms. We also detect unresolved ¹³CO (J = 2 ‑ 1) line emission toward the nuclear region, southern bar end, and in a relatively isolated clump in the southern portion of the galaxy, while no C¹⁸O(J = 2 ‑ 1) line emission is detected at a 3σ rms noise level of 42 mJy beam^‑1 per 20 km s^‑1 channel. Using RADEX modeling with a large velocity gradient approximation, we derive kinetic temperatures ranging from ∼5 to 10 K (in the spiral arms) to ∼25 K (at the center) and H₂ number densities from ∼400 to 1000 cm^‑3 (in the spiral arms) to ∼12,500 cm^‑3 (at the center). From this density modeling, we find a total H₂ mass of 9.6 × 10⁹ M _⊙, which is ∼50% higher than previous estimates made using a constant H₂–CO conversion factor, but is largely dependent on the assumed vertical distribution of the CO gas. With the exception of the nuclear region, we also identify a tentative correlation between star formation efficiency and kinetic temperature. We derive a galactic rotation curve, finding a peak velocity of ∼207 km s^‑1 and estimate a total dynamical mass of 4.94 ± 0.70 × 10¹⁰ M _⊙ at a galactocentric radius of ∼6.2 kpc (121″).

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 (&gsim; 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 (&tilde;4" or &tilde;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: 144819
Type: article
Authors: Herczeg, Gregory J.; Johnstone, Doug; Mairs, Steve; Hatchell, Jennifer; Lee, Jeong-Eun; Bower, Geoffrey C.; Chen, Huei-Ru Vivien; Aikawa, Yuri; Yoo, Hyunju; Kang, Sung-ju; Kang, Miju; Chen, Wen-Ping; Williams, Jonathan P.; Bae, Jaehan; Dunham, Michael M.; Vorobyov, Eduard I.; Zhu, Zhaohuan; Rao, Ramprasad; Kirk, Helen; Takahashi, Satoko; Morata, Oscar; Lacaille, Kevin; Lane, James; Pon, Andy; Scholz, Aleks; Samal, Manash R.; Bell, Graham S.; Graves, Sarah; Lee, E. 'lisa M.; Parsons, Harriet; He, Yuxin; Zhou, Jianjun; Kim, Mi-Ryang; Chapman, Scott; Drabek-Maunder, Emily; Chung, Eun Jung; Eyres, Stewart P. S.; Forbrich, Jan; Hillenbrand, Lynne A.; Inutsuka, Shu-ichiro; Kim, Gwanjeong; Kim, Kyoung Hee; Kuan, Yi-Jehng; Kwon, Woojin; Lai, Shih-Ping; Lalchand, Bhavana; Lee, Chang Won; Lee, Chin-Fei; Long, Feng; Lyo, A. -Ran; Qian, Lei; Scicluna, Peter; Soam, Archana; Stamatellos, Dimitris; Takakuwa, Shigehisa; Tang, Ya-Wen; Wang, Hongchi; Wang, Yiren
Abstract: Most protostars have luminosities that are fainter than expected from steady accretion over the protostellar lifetime. The solution to this problem may lie in episodic mass accretion-prolonged periods of very low accretion punctuated by short bursts of rapid accretion. However, the timescale and amplitude for variability at the protostellar phase is almost entirely unconstrained. In A James Clerk Maxwell Telescope/SCUBA-2 Transient Survey of Protostars in Nearby Star-forming Regions, we are monitoring monthly with SCUBA-2 the submillimeter emission in eight fields within nearby (² includes ~105 peaks with peaks brighter than 0.5 Jy/beam (43 associated with embedded protostars or disks) and 237 peaks of 0.125-0.5 Jy/beam (50 with embedded protostars or disks). Each field has enough bright peaks for flux calibration relative to other peaks in the same field, which improves upon the nominal flux calibration uncertainties of submillimeter observations to reach a precision of ~2%-3% rms, and also provides quantified confidence in any measured variability. The timescales and amplitudes of any submillimeter variation will then be converted into variations in accretion rate and subsequently used to infer the physical causes of the variability. This survey is the first dedicated survey for submillimeter variability and complements other transient surveys at optical and near-IR wavelengths, which are not sensitive to accretion variability of deeply embedded protostars.

ID: 144776
Type: article
Authors: Hull, Charles L. H.; Girart, Josep M.; Tychoniec, Lukasz; Rao, Ramprasad; Cortés, Paulo C.; Pokhrel, Riwaj; Zhang, Qizhou; Houde, Martin; Dunham, Michael M.; Kristensen, Lars E.; Lai, Shih-Ping; Li, Zhi-Yun; Plambeck, Richard L.
Abstract: We present high angular resolution dust polarization and molecular line observations carried out with the Atacama Large Millimeter/submillimeter Array (ALMA) toward the Class 0 protostar Serpens SMM1. By complementing these observations with new polarization observations from the Submillimeter Array (SMA) and archival data from the Combined Array for Research in Millimeter-wave Astronomy (CARMA) and the James Clerk Maxwell Telescopes (JCMT), we can compare the magnetic field orientations at different spatial scales. We find major changes in the magnetic field orientation between large (~0.1 pc) scales-where the magnetic field is oriented E-W, perpendicular to the major axis of the dusty filament where SMM1 is embedded-and the intermediate and small scales probed by CARMA (~1000 au resolution), the SMA (~350 au resolution), and ALMA (~140 au resolution). The ALMA maps reveal that the redshifted lobe of the bipolar outflow is shaping the magnetic field in SMM1 on the southeast side of the source; however, on the northwestern side and elsewhere in the source, low-velocity shocks may be causing the observed chaotic magnetic field pattern. High-spatial-resolution continuum and spectral-line observations also reveal a tight (~130 au) protobinary system in SMM1-b, the eastern component of which is launching an extremely high-velocity, one-sided jet visible in both {CO}(J=2\to 1) and {SiO}(J=5\to 4); however, that jet does not appear to be shaping the magnetic field. These observations show that with the sensitivity and resolution of ALMA, we can now begin to understand the role that feedback (e.g., from protostellar outflows) plays in shaping the magnetic field in very young, star-forming sources like SMM1.

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: 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.