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Satoshi Yamamoto - One of the best experts on this subject based on the ideXlab platform.
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orion alma new generation survey oranges i dust continuum and free free emission of omc 2 3 filament Protostars
Astronomy and Astrophysics, 2021Co-Authors: Mathilde Bouvier, Nami Sakai, Satoshi Yamamoto, A Lopezsepulcre, C Ceccarelli, Yaolun YangAbstract:Context. The spectral energy distribution (SED) in the millimetre to centimetre range is an extremely useful tool for characterising the dust in protostellar envelopes as well as free-free emission from the protostar and outflow. Actually, the evolutionary status of solar-type Protostars is often based on their SED in the near-infrared to millimetre range. In addition, the presence or absence of free-free emission can be considered an indicator of the source evolutionary stage (Class 0/I versus Class II/III). While many studies have been carried out towards low- and high-mass Protostars, little exists so far about solar-type Protostars in high-mass star-forming regions, which are likely to be representatives of the conditions where the Solar System was born.Aims. In this work, we focus on the embedded solar-type Protostars in the Orion Molecular Cloud (OMC) 2 and 3 filaments, which are bounded by nearby HII regions and which are, therefore, potentially affected by the high-UV illumination of the nearby OB stars. We use various dust parameters to understand whether the small-scale structure (≤1000 au) and the evolutionary status of these solar-type Protostars are affected by the nearby HII regions, as is the case for the large-scale (≤104 au) gas chemical composition.Methods. We used the Atacama Large (sub-)Millimeter Array (ALMA) in the 1.3 mm band (246.2 GHz) to image the continuum of 16 young (Class 0/I) OMC-2/3 solar-type Protostars, with an angular resolution of 0.25″ (100 au). We completed our data with archival data from the ALMA and VLA VANDAM survey of Orion Protostars at 333 and 32.9 GHz, respectively, to construct the dust SED and extract the dust temperature, the dust emissivity spectral index, the envelope plus disk mass of the sources and to assess whether free-free emission is contaminating their dust SED in the centimetre range.Results. From the millimetre to centimetre range dust SED, we found low dust emissivity spectral indexes (β Our results show that the small-scale dust properties of the embedded OMC-2/3 Protostars are not affected by the high-UV illumination from the nearby HII regions and that the formation of Protostars likely takes place simultaneously throughout the filament.
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orion alma new generation survey oranges i dust continuum and free free emission of omc 2 3 filament Protostars
arXiv: Astrophysics of Galaxies, 2021Co-Authors: Mathilde Bouvier, Nami Sakai, Satoshi Yamamoto, A Lopezsepulcre, C Ceccarelli, Yaolun YangAbstract:The spectral energy distribution (SED) in the millimetre (mm) to centimetre (cm) range is a useful tool for characterising the dust in protostellar envelopes as well as free-free emission from the protostar and outflow. While many studies have been carried out towards low- and high-mass Protostars, little exists so far about solar-type Protostars in high-mass star-forming regions, which are likely to be representatives of the conditions where the Solar System was born. We focus here on the OMC-2/3 solar-type Protostars, which are bounded by nearby HII regions and which are, therefore, potentially affected by the high-UV illumination. We aim to understand whether the small-scale structure ($\leq$1000 au) and the evolutionary status of these solar-type Protostars are affected by the nearby HII regions, as is the case for the large-scale ($\leq$10$^4$ au) gas chemical composition. We used ALMA in the 1.3 mm band (246.2 GHz) to image the continuum of 16 OMC-2/3 solar-type Protostars, with an angular resolution of 0.25$''$ (100 au). We completed our data with archival data from the VANDAM survey of Orion Protostars at 333 and 32.9 GHz, respectively, to construct the dust SED, extract several dust parameters and to assess whether free-free emission is contaminating their dust SED in the cm range. From the mm to cm range dust SED, we found low dust emissivity spectral indexes ($\beta < 1$) for the majority of our source sample and free-free emission towards only 5 of the 16 sample sources. We were also able to confirm or correct the evolutionary status of the source sample. Finally, we did not find any dependence of the source dust parameters on their location in the OMC-2/3 filament. Our results show that the small-scale dust properties of the OMC-2/3 Protostars are not affected by the high- UV illumination from the nearby HII regions.
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discovery of striking difference of molecular emission line richness in the potential proto binary system ngc 2264 cmm3
The Astrophysical Journal, 2017Co-Authors: Nami Sakai, A Lopezsepulcre, Yoshimasa Watanabe, Takeshi Sakai, Tomoya Hirota, Shengyuan Liu, Satoshi YamamotoAbstract:We have conducted an interferometric line survey in the 0.8 mm band toward the young high-mass protostar candidate NGC 2264 CMM3 with ALMA. CMM3 is resolved into the two continuum peaks, CMM3A and CMM3B, at an angular separation of . Thus, CMM3 is found to be a binary system candidate. We have detected molecular outflows associated with CMM3A and CMM3B each, indicating active star formation. In addition to the two peaks, six faint continuum peaks are detected around CMM3A and CMM3B, most of which are thought to be evolved low-mass Protostars. CMM3A is found to be rich in molecular line emission including complex organic molecules such as HCOOCH3 and CH3OCH3. The emission of complex organic molecules is distributed within a compact region around the continuum peak of CMM3A. Hence, CMM3A apparently harbors a hot core. On the other hand, CMM3B is deficient in molecular line emission, although its continuum flux is almost comparable to that of CMM3A. Possible origins of the striking difference between CMM3A and CMM3B are discussed.
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probing the effects of external irradiation on low mass Protostars through unbiased line surveys
arXiv: Solar and Stellar Astrophysics, 2015Co-Authors: J K Jorgensen, Nami Sakai, Johan E Lindberg, Yoshimasa Watanabe, Suzanne E Bisschop, Satoshi YamamotoAbstract:(abridged) Context: The envelopes of molecular gas around embedded low-mass Protostars show different chemistries, which can be used to trace their formation history and physical conditions. The excitation of some molecular species can also be used to trace these physical conditions, making it possible to constrain e.g. sources of heating and excitation. Aims: To study the range of influence of an intermediate-mass Herbig Be protostar, and to find what chemical and physical impact feedback effects from the environment may have on embedded Protostars. Methods: We follow up on an earlier line survey of the Class 0/I source R CrA IRS7B in the 0.8 mm window with an unbiased line survey of the same source in the 1.3 mm window using the APEX telescope. We also study the excitation of the key species H2CO, CH3OH, and c-C3H2 in a complete sample of the 18 embedded Protostars in the Corona Australis star-forming region. Radiative transfer models are used to establish abundances of the molecular species. Results: We detect line emission from 20 molecular species (32 including isotopologues) in the two surveys. The most complex species detected are CH3OH, CH3CCH, CH3CHO, and CH3CN. Several complex organics are significantly under-abundant in comparison with "hot corino" Protostars. The H2CO temperatures of the sources in the region decrease with the distance to the Herbig Be star R CrA, whereas the c-C3H2 temperatures remain constant across the star-forming region. Conclusions: The high H2CO temperatures observed towards objects close to R CrA suggest that this star has a sphere of influence of several 10000 AU in which it increases the temperature of the molecular gas to 30-50 K through irradiation. The chemistry in the IRS7B envelope differs significantly from many other embedded Protostars, which could be an effect of the external irradiation from R CrA.
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a recent accretion burst in the low mass protostar iras 15398 3359 alma imaging of its related chemistry
The Astrophysical Journal, 2013Co-Authors: J K Jorgensen, R Visser, Nami Sakai, Edwin A Bergin, C Brinch, Daniel Harsono, Johan E Lindberg, Ewine F Van Dishoeck, Satoshi YamamotoAbstract:Low-mass Protostars have been suggested to show highly variable accretion rates throughout their evolution. Such changes in accretion, and related heating of their ambient envelopes, may trigger significant chemical variations on different spatial scales and from source-to-source. We present images of emission from C17O, H13CO+, CH3OH, C34S and C2H toward the low-mass protostar IRAS 15398-3359 on 0.''5 (75 AU diameter) scales with the Atacama Large Millimeter/submillimeter Array at 340 GHz. The resolved images show that the emission from H13CO+ is only present in a ring-like structure with a radius of about 1-1.''5 (150-200 AU) whereas the CO and other high dipole moment molecules are centrally condensed toward the location of the central protostar. We propose that HCO+ is destroyed by water vapor present on small scales. The origin of this water vapor is likely an accretion burst during the last 100-1000 yr increasing the luminosity of IRAS 15398-3359 by a factor of 100 above its current luminosity. Such a burst in luminosity can also explain the centrally condensed CH3OH and extended warm carbon-chain chemistry observed in this source and furthermore be reflected in the relative faintness of its compact continuum emission compared to other Protostars.
Nami Sakai - One of the best experts on this subject based on the ideXlab platform.
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orion alma new generation survey oranges i dust continuum and free free emission of omc 2 3 filament Protostars
Astronomy and Astrophysics, 2021Co-Authors: Mathilde Bouvier, Nami Sakai, Satoshi Yamamoto, A Lopezsepulcre, C Ceccarelli, Yaolun YangAbstract:Context. The spectral energy distribution (SED) in the millimetre to centimetre range is an extremely useful tool for characterising the dust in protostellar envelopes as well as free-free emission from the protostar and outflow. Actually, the evolutionary status of solar-type Protostars is often based on their SED in the near-infrared to millimetre range. In addition, the presence or absence of free-free emission can be considered an indicator of the source evolutionary stage (Class 0/I versus Class II/III). While many studies have been carried out towards low- and high-mass Protostars, little exists so far about solar-type Protostars in high-mass star-forming regions, which are likely to be representatives of the conditions where the Solar System was born.Aims. In this work, we focus on the embedded solar-type Protostars in the Orion Molecular Cloud (OMC) 2 and 3 filaments, which are bounded by nearby HII regions and which are, therefore, potentially affected by the high-UV illumination of the nearby OB stars. We use various dust parameters to understand whether the small-scale structure (≤1000 au) and the evolutionary status of these solar-type Protostars are affected by the nearby HII regions, as is the case for the large-scale (≤104 au) gas chemical composition.Methods. We used the Atacama Large (sub-)Millimeter Array (ALMA) in the 1.3 mm band (246.2 GHz) to image the continuum of 16 young (Class 0/I) OMC-2/3 solar-type Protostars, with an angular resolution of 0.25″ (100 au). We completed our data with archival data from the ALMA and VLA VANDAM survey of Orion Protostars at 333 and 32.9 GHz, respectively, to construct the dust SED and extract the dust temperature, the dust emissivity spectral index, the envelope plus disk mass of the sources and to assess whether free-free emission is contaminating their dust SED in the centimetre range.Results. From the millimetre to centimetre range dust SED, we found low dust emissivity spectral indexes (β Our results show that the small-scale dust properties of the embedded OMC-2/3 Protostars are not affected by the high-UV illumination from the nearby HII regions and that the formation of Protostars likely takes place simultaneously throughout the filament.
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orion alma new generation survey oranges i dust continuum and free free emission of omc 2 3 filament Protostars
arXiv: Astrophysics of Galaxies, 2021Co-Authors: Mathilde Bouvier, Nami Sakai, Satoshi Yamamoto, A Lopezsepulcre, C Ceccarelli, Yaolun YangAbstract:The spectral energy distribution (SED) in the millimetre (mm) to centimetre (cm) range is a useful tool for characterising the dust in protostellar envelopes as well as free-free emission from the protostar and outflow. While many studies have been carried out towards low- and high-mass Protostars, little exists so far about solar-type Protostars in high-mass star-forming regions, which are likely to be representatives of the conditions where the Solar System was born. We focus here on the OMC-2/3 solar-type Protostars, which are bounded by nearby HII regions and which are, therefore, potentially affected by the high-UV illumination. We aim to understand whether the small-scale structure ($\leq$1000 au) and the evolutionary status of these solar-type Protostars are affected by the nearby HII regions, as is the case for the large-scale ($\leq$10$^4$ au) gas chemical composition. We used ALMA in the 1.3 mm band (246.2 GHz) to image the continuum of 16 OMC-2/3 solar-type Protostars, with an angular resolution of 0.25$''$ (100 au). We completed our data with archival data from the VANDAM survey of Orion Protostars at 333 and 32.9 GHz, respectively, to construct the dust SED, extract several dust parameters and to assess whether free-free emission is contaminating their dust SED in the cm range. From the mm to cm range dust SED, we found low dust emissivity spectral indexes ($\beta < 1$) for the majority of our source sample and free-free emission towards only 5 of the 16 sample sources. We were also able to confirm or correct the evolutionary status of the source sample. Finally, we did not find any dependence of the source dust parameters on their location in the OMC-2/3 filament. Our results show that the small-scale dust properties of the OMC-2/3 Protostars are not affected by the high- UV illumination from the nearby HII regions.
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discovery of striking difference of molecular emission line richness in the potential proto binary system ngc 2264 cmm3
The Astrophysical Journal, 2017Co-Authors: Nami Sakai, A Lopezsepulcre, Yoshimasa Watanabe, Takeshi Sakai, Tomoya Hirota, Shengyuan Liu, Satoshi YamamotoAbstract:We have conducted an interferometric line survey in the 0.8 mm band toward the young high-mass protostar candidate NGC 2264 CMM3 with ALMA. CMM3 is resolved into the two continuum peaks, CMM3A and CMM3B, at an angular separation of . Thus, CMM3 is found to be a binary system candidate. We have detected molecular outflows associated with CMM3A and CMM3B each, indicating active star formation. In addition to the two peaks, six faint continuum peaks are detected around CMM3A and CMM3B, most of which are thought to be evolved low-mass Protostars. CMM3A is found to be rich in molecular line emission including complex organic molecules such as HCOOCH3 and CH3OCH3. The emission of complex organic molecules is distributed within a compact region around the continuum peak of CMM3A. Hence, CMM3A apparently harbors a hot core. On the other hand, CMM3B is deficient in molecular line emission, although its continuum flux is almost comparable to that of CMM3A. Possible origins of the striking difference between CMM3A and CMM3B are discussed.
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probing the effects of external irradiation on low mass Protostars through unbiased line surveys
arXiv: Solar and Stellar Astrophysics, 2015Co-Authors: J K Jorgensen, Nami Sakai, Johan E Lindberg, Yoshimasa Watanabe, Suzanne E Bisschop, Satoshi YamamotoAbstract:(abridged) Context: The envelopes of molecular gas around embedded low-mass Protostars show different chemistries, which can be used to trace their formation history and physical conditions. The excitation of some molecular species can also be used to trace these physical conditions, making it possible to constrain e.g. sources of heating and excitation. Aims: To study the range of influence of an intermediate-mass Herbig Be protostar, and to find what chemical and physical impact feedback effects from the environment may have on embedded Protostars. Methods: We follow up on an earlier line survey of the Class 0/I source R CrA IRS7B in the 0.8 mm window with an unbiased line survey of the same source in the 1.3 mm window using the APEX telescope. We also study the excitation of the key species H2CO, CH3OH, and c-C3H2 in a complete sample of the 18 embedded Protostars in the Corona Australis star-forming region. Radiative transfer models are used to establish abundances of the molecular species. Results: We detect line emission from 20 molecular species (32 including isotopologues) in the two surveys. The most complex species detected are CH3OH, CH3CCH, CH3CHO, and CH3CN. Several complex organics are significantly under-abundant in comparison with "hot corino" Protostars. The H2CO temperatures of the sources in the region decrease with the distance to the Herbig Be star R CrA, whereas the c-C3H2 temperatures remain constant across the star-forming region. Conclusions: The high H2CO temperatures observed towards objects close to R CrA suggest that this star has a sphere of influence of several 10000 AU in which it increases the temperature of the molecular gas to 30-50 K through irradiation. The chemistry in the IRS7B envelope differs significantly from many other embedded Protostars, which could be an effect of the external irradiation from R CrA.
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a recent accretion burst in the low mass protostar iras 15398 3359 alma imaging of its related chemistry
The Astrophysical Journal, 2013Co-Authors: J K Jorgensen, R Visser, Nami Sakai, Edwin A Bergin, C Brinch, Daniel Harsono, Johan E Lindberg, Ewine F Van Dishoeck, Satoshi YamamotoAbstract:Low-mass Protostars have been suggested to show highly variable accretion rates throughout their evolution. Such changes in accretion, and related heating of their ambient envelopes, may trigger significant chemical variations on different spatial scales and from source-to-source. We present images of emission from C17O, H13CO+, CH3OH, C34S and C2H toward the low-mass protostar IRAS 15398-3359 on 0.''5 (75 AU diameter) scales with the Atacama Large Millimeter/submillimeter Array at 340 GHz. The resolved images show that the emission from H13CO+ is only present in a ring-like structure with a radius of about 1-1.''5 (150-200 AU) whereas the CO and other high dipole moment molecules are centrally condensed toward the location of the central protostar. We propose that HCO+ is destroyed by water vapor present on small scales. The origin of this water vapor is likely an accretion burst during the last 100-1000 yr increasing the luminosity of IRAS 15398-3359 by a factor of 100 above its current luminosity. Such a burst in luminosity can also explain the centrally condensed CH3OH and extended warm carbon-chain chemistry observed in this source and furthermore be reflected in the relative faintness of its compact continuum emission compared to other Protostars.
Takashi Hosokawa - One of the best experts on this subject based on the ideXlab platform.
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massive outflows driven by magnetic effects in star forming clouds with high mass accretion rates
Monthly Notices of the Royal Astronomical Society, 2017Co-Authors: Yuko Matsushita, Masahiro N Machida, Takashi Hosokawa, Yuya SakuraiAbstract:The relation between the mass accretion rate onto the circumstellar disc and the rate of mass ejection by magnetically driven winds is investigated using three-dimensional magnetohydrodynamics simulations. Using a spherical cloud core with a varying ratio of thermal to gravitational energy, which determines the mass accretion rate onto the disc, to define the initial conditions, the outflow propagation for approximately 10^4 yr after protostar formation is then calculated for several cloud cores. The mass ejection rate and accretion rate are comparable only when the magnetic energy of the initial cloud core is comparable to the gravitational energy. Consequently, in strongly magnetised clouds a higher mass accretion rate naturally produces both massive Protostars and massive outflows. The simulated outflow mass, momentum, kinetic energy and momentum flux agree well with observations, indicating that massive stars form through the same mechanism as low-mass stars but require a significantly strong magnetic field to launch massive outflows.
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formation of massive primordial stars intermittent uv feedback with episodic mass accretion
arXiv: Astrophysics of Galaxies, 2015Co-Authors: Takashi Hosokawa, Harold W Yorke, Kazuyuki Omukai, Shingo Hirano, Rolf Kuiper, Naoki YoshidaAbstract:We present coupled stellar evolution (SE) and 3D radiation-hydrodynamic (RHD) simulations of the evolution of primordial Protostars, their immediate environment, and the dynamic accretion history under the influence of stellar ionizing and dissociating UV feedback. Our coupled SE-RHD calculations result in a wide diversity of final stellar masses covering 10 Msun $\lesssim M_* \lesssim$ 1000 Msun. The formation of very massive ($\gtrsim$ 250 Msun) stars is possible under weak UV feedback, whereas ordinary massive (a few x 10 Msun) stars form when UV feedback can efficiently halt the accretion. This may explain the peculiar abundance pattern of a Galactic metal-poor star recently reported by Aoki et al. (2014), possibly the observational signature of very massive precursor primordial stars. Weak UV feedback occurs in cases of variable accretion, in particular when repeated short accretion bursts temporarily exceed 0.01 Msun/yr, causing the protostar to inflate. In the bloated state, the protostar has low surface temperature and UV feedback is suppressed until the star eventually contracts, on a thermal adjustment timescale, to create an HII region. If the delay time between successive accretion bursts is sufficiently short, the protostar remains bloated for extended periods, initiating at most only short periods of UV feedback. Disk fragmentation does not necessarily reduce the final stellar mass. Quite the contrary, we find that disk fragmentation enhances episodic accretion as many fragments migrate inward and are accreted onto the star, thus allowing continued stellar mass growth under conditions of intermittent UV feedback. This trend becomes more prominent as we improve the resolution of our simulations. We argue that simulations with significantly higher resolution than reported previously are needed to derive accurate gas mass accretion rates onto primordial Protostars.
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radiation transfer of models of massive star formation iii the evolutionary sequence
The Astrophysical Journal, 2014Co-Authors: Yichen Zhang, Jonathan C Tan, Takashi HosokawaAbstract:We present radiation transfer simulations of evolutionary sequences of massive Protostars forming from massive dense cores in environments of high mass surface densities, based on the Turbulent Core Model. The protostellar evolution is calculated with a multi-zone numerical model, with the accretion rate regulated by feedback from an evolving disk wind outflow cavity. The disk evolution is calculated assuming a fixed ratio of disk to protostellar mass, while the core envelope evolution assumes an inside-out collapse of the core with a fixed outer radius. In this framework, an evolutionary track is determined by three environmental initial conditions: the core mass Mc , the mass surface density of the ambient clump Σcl, and the ratio of the core's initial rotational to gravitational energy β c . Evolutionary sequences with various Mc , Σcl, and β c are constructed. We find that in a fiducial model with Mc = 60 M ☉, Σcl = 1 g cm–2, and β c = 0.02, the final mass of the protostar reaches at least ~26 M ☉, making the final star formation efficiency 0.43. For each of the evolutionary tracks, radiation transfer simulations are performed at selected stages, with temperature profiles, spectral energy distributions (SEDs), and multiwavelength images produced. At a given stage, the envelope temperature depends strongly on Σcl, with higher temperatures in a higher Σcl core, but only weakly on Mc . The SED and MIR images depend sensitively on the evolving outflow cavity, which gradually widens as the protostar grows. The fluxes at 100 μm increase dramatically, and the far-IR peaks move to shorter wavelengths. The influence of Σcl and β c (which determines disk size) are discussed. We find that, despite scatter caused by different Mc , Σcl, β c , and inclinations, sources at a given evolutionary stage appear in similar regions of color-color diagrams, especially when using colors with fluxes at 70 μm, where scatter due to inclination is minimized, implying that such diagrams can be useful diagnostic tools for identifying the evolutionary stages of massive Protostars. We discuss how intensity profiles along or perpendicular to the outflow axis are affected by environmental conditions and source evolution and can thus act as additional diagnostics of the massive star formation process.
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direct diagnostics of forming massive stars stellar pulsation and periodic variability of maser sources
The Astrophysical Journal, 2013Co-Authors: Kohei Inayoshi, Takashi Hosokawa, Koichiro Sugiyama, Kazuhito Motogi, Kei E I TanakaAbstract:The 6.7 GHz methanol maser emission, a tracer of forming massive stars, sometimes shows enigmatic periodic flux variations over several 10-100 days. In this Letter, we propose that these periodic variations could be explained by the pulsation of massive Protostars growing under rapid mass accretion with rates of . Our stellar evolution calculations predict that the massive Protostars have very large radii exceeding 100 R ☉ at maximum, and here we study the pulsational stability of such bloated Protostars by way of the linear stability analysis. We show that the protostar becomes pulsationally unstable with various periods of several 10-100 days depending on different accretion rates. With the fact that the stellar luminosity when the star is pulsationally unstable also depends on the accretion rate, we derive the period-luminosity relation log (L/ L ☉) = 4.62 + 0.98log (P/100 days), which is testable with future observations. Our models further show that the radius and mass of the pulsating massive protostar should also depend on the period. It would be possible to infer such protostellar properties and the accretion rate with the observed period. Measuring the maser periods enables a direct diagnosis of the structure of accreting massive Protostars, which are deeply embedded in dense gas and are inaccessible with other observations.
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direct diagnostics of forming massive stars stellar pulsation and periodic variability of maser sources
arXiv: Solar and Stellar Astrophysics, 2013Co-Authors: Kohei Inayoshi, Takashi Hosokawa, Koichiro Sugiyama, Kazuhito Motogi, Kei E I TanakaAbstract:The 6.7 GHz methanol maser emission, a tracer of forming massive stars, sometimes shows enigmatic periodic flux variations over several 10-100 days. In this Letter, we propose that this periodic variations could be explained by the pulsation of massive Protostars growing under rapid mass accretion with rates of Mdot > 10^-3 Msun/yr. Our stellar evolution calculations predict that the massive Protostars have very large radius exceeding 100 Rsun at maximum, and we here study the pulsational stability of such the bloated Protostars by way of the linear stability analysis. We show that the protostar becomes pulsationally unstable with various periods of several 10-100 days, depending on different accretion rates. With the fact that the stellar luminosity when the star is pulsationally unstable also depends on the accretion rate, we derive the period-luminosity relation log (L/Lsun) = 4.62 + 0.98log(P/100 day), which is testable with future observations. Our models further show that the radius and mass of the pulsating massive protostar should also depend on the period. It would be possible to infer such protostellar properties and the accretion rate with the observed period. Measuring the maser periods enables a direct diagnosis of the structure of accreting massive Protostars, which are deeply embedded in dense gas and inaccessible with other observations.
John J Tobin - One of the best experts on this subject based on the ideXlab platform.
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the herschel orion protostar survey far infrared photometry and colors of Protostars and their variations across orion a and b
The Astrophysical Journal, 2020Co-Authors: William J Fischer, Amelia M Stutz, John J Tobin, Thomas Stanke, Thomas S Megeath, James Di Francesco, Mayra Osorio, Elise Furlan, P Manoj, Lori AllenAbstract:The degree to which the properties of Protostars are affected by environment remains an open question. To investigate this, we look at the Orion A and B molecular clouds, home to most of the Protostars within 500 pc. At ~400 pc, Orion is close enough to distinguish individual Protostars across a range of environments in terms of both the stellar and gas projected densities. As part of the Herschel Orion Protostar Survey (HOPS), we used the Photodetector Array Camera and Spectrometer to map 108 partially overlapping square fields with edge lengths of 5' or 8' and measure the 70 and 160 μm flux densities of 338 Protostars within them. In this paper we examine how these flux densities and their ratio depend on evolutionary state and environment within the Orion complex. We show that Class 0 Protostars occupy a region of the 70 μm flux density versus 160 μm/70 μm flux density ratio diagram that is distinct from their more evolved counterparts. We then present evidence that the Integral-Shaped Filament (ISF) and Orion B contain Protostars with more massive inner envelopes than those in the more sparsely populated LDN 1641 region. This can be interpreted as evidence for increasing star formation rates in the ISF and Orion B or as a tendency for more massive inner envelopes to be inherited from denser birth environments. We also provide technical details about the mapmaking and photometric procedures used in the HOPS program.
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the herschel orion protostar survey far infrared photometry and colors of Protostars and their variations across orion a and b
arXiv: Astrophysics of Galaxies, 2020Co-Authors: William J Fischer, Amelia M Stutz, John J Tobin, Thomas Stanke, Thomas S Megeath, James Di Francesco, Mayra Osorio, Elise Furlan, P Manoj, Lori AllenAbstract:The degree to which the properties of Protostars are affected by environment remains an open question. To investigate this, we look at the Orion A and B molecular clouds, home to most of the Protostars within 500 pc. At ~400 pc, Orion is close enough to distinguish individual Protostars across a range of environments in terms of both the stellar and gas projected densities. As part of the Herschel Orion Protostar Survey (HOPS), we used the Photodetector Array Camera and Spectrometer (PACS) to map 108 partially overlapping square fields with edge lengths of 5 arcmin or 8 arcmin and measure the 70 micron and 160 micron flux densities of 338 Protostars within them. In this paper we examine how these flux densities and their ratio depend on evolutionary state and environment within the Orion complex. We show that Class 0 Protostars occupy a region of the 70 micron flux density versus 160 micron to 70 micron flux density ratio diagram that is distinct from their more evolved counterparts. We then present evidence that the Integral-Shaped Filament (ISF) and Orion B contain Protostars with more massive envelopes than those in the more sparsely populated LDN 1641 region. This can be interpreted as evidence for increasing star formation rates in the ISF and Orion B or as a tendency for more massive envelopes to be inherited from denser birth environments. We also provide technical details about the map-making and photometric procedures used in the HOPS program.
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the vla nascent disk and multiplicity survey of perseus Protostars vandam v 18 candidate disks around class 0 and i Protostars in the perseus molecular cloud
arXiv: Solar and Stellar Astrophysics, 2018Co-Authors: Dominique Seguracox, John J Tobin, Leslie W Looney, Robert J Harris, Sarah Sadavoy, Michael M DunhamAbstract:We present the full disk-fit results VANDAM survey of all Class 0 and I Protostars in the Perseus molecular cloud. We have 18 new protostellar disk candidates around Class 0 and I sources, which are well described by a simple, parametrized disk model fit to the 8 mm VLA dust-continuum observations. 33% of Class 0 Protostars and just 11% of Class I Protostars have candidate disks, while 78% of Class 0 and I Protostars do not have signs of disks within our 12 AU disk diameter resolution limit, indicating that at 8 mm most disks in the Class 0 and I phases are <10 AU in radius. These small radii may be a result of surface brightness sensitivity limits. Modeled 8 mm radii are similar to the radii of known Class 0 disks with detected Keplerian rotation. Since our 8 mm data trace a population of larger dust grains which radially drift towards the protostar and are lower limits on true disk sizes, large disks at early times do not seem to be particularly rare. We find statistical evidence that Class 0 and I disks are likely drawn from the same distribution, meaning disk properties may be defined early in the Class 0 phase and do not undergo large changes through the Class I phase. By combining our candidate disk properties with previous polarization observations, we find a qualitative indication that misalignment between inferred envelope-scale magnetic fields and outflows may indicate disks on smaller scales in Class 0 sources.
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a sub arcsecond survey toward class 0 Protostars in perseus searching for signatures of protostellar disks
The Astrophysical Journal, 2015Co-Authors: John J Tobin, Hsinfang Chiang, David J Wilner, Leslie W Looney, Laurent Loinard, Tyler L Bourke, Claire J Chandler, Woojin Kwon, Scott SchneeAbstract: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 () 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.
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the magnetic field in the class 0 protostellar disk of l1527
The Astrophysical Journal, 2014Co-Authors: Dominique Seguracox, John J Tobin, Leslie W Looney, Woojin Kwon, Ian W Stephens, Manuel Fernandezlopez, Richard M CrutcherAbstract:We present subarcsecond (~0.''35) resolved observations of the 1.3 mm dust polarization from the edge-on circumstellar disk around the Class 0 protostar L1527. The inferred magnetic field is consistent with a dominantly toroidal morphology; there is no significantly detected vertical poloidal component to which observations of an edge-on disk are most sensitive. This suggests that angular momentum transport in Class 0 Protostars (when large amounts of material are fed down to the disk from the envelope and accreted onto the protostar) is driven mainly by magnetorotational instability rather than magnetocentrifugal winds at 50 AU scales. In addition, with the data to date there is an early, tentative trend that R > 30 AU disks have so far been found in Class 0 systems with average magnetic fields on the 1000 AU scale strongly misaligned with the rotation axis. The absence of such a disk in the aligned case could be due to efficient magnetic braking that disrupts disk formation. If this is the case, this implies that candidate Class 0 disk systems could be identified by the average magnetic field direction at ~1000 AU spatial scales.
J K Jorgensen - One of the best experts on this subject based on the ideXlab platform.
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the mass evolution of protostellar disks and envelopes in the perseus molecular cloud
arXiv: Solar and Stellar Astrophysics, 2019Co-Authors: B C Andersen, Dominique Seguracox, J K Jorgensen, Michael M Dunham, Ian W Stephens, Riwaj Pokhrel, Soren Frimann, Philip C MyersAbstract: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 J{\o}rgensen et al. (2009) to obtain mass measurements of disks and envelopes around embedded Protostars with observations that do not resolve the disk (resolution of $\sim$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 (VANDAM) 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.
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the alma pils survey first detections of ethylene oxide acetone and propanal toward the low mass protostar iras 16293 2422
Astronomy and Astrophysics, 2017Co-Authors: J. M. Lykke, A Coutens, J K Jorgensen, Tyler L Bourke, M H D Van Der Wiel, R T Garrod, Holger S P Muller, P Bjerkeli, H CalcuttAbstract:Context. One of the open questions in astrochemistry is how complex organic and prebiotic molecules are formed. The unsurpassed sensitivity of the Atacama Large Millimeter/submillimeter Array (ALMA) takes the quest for discovering molecules in the warm and dense gas surrounding young stars to the next level. Aims. Our aim is to start the process of compiling an inventory of oxygen-bearing complex organic molecules toward the solar-type Class 0 protostellar binary IRAS 16293-2422 from an unbiased spectral survey with ALMA, Protostellar Interferometric Line Survey (PILS). Here we focus on the new detections of ethylene oxide (c-C2H4O), acetone (CH3COCH3), and propanal (C2H5CHO). Methods. With ALMA, we surveyed the spectral range from 329 to 363 GHz at 0.5? (60 AU diameter) resolution. Using a simple model for the molecular emission in local thermodynamical equilibrium, the excitation temperatures and column densities of each species were constrained. Results. We successfully detect propanal (44 lines), ethylene oxide (20 lines) and acetone (186 lines) toward one component of the protostellar binary, IRAS 16293B. The high resolution maps demonstrate that the emission for all investigated species originates from the compact central region close to the protostar. This, along with a derived common excitation temperature of Tex ? 125 K, is consistent with a coexistence of these molecules in the same gas. Conclusions. The observations mark the first detections of acetone, propanal and ethylene oxide toward a low-mass protostar. The relative abundance ratios of the two sets of isomers, a CH3COCH3/C2H5CHO ratio of 8 and a CH3CHO/c-C2H4O ratio of 12, are comparable to previous observations toward high-mass Protostars. The majority of observed abundance ratios from these results as well as those measured toward high-mass Protostars are up to an order of magnitude above the predictions from chemical models. This may reflect either missing reactions or uncertain rates in the chemical networks. The physical conditions, such as temperatures or densities, used in the models, may not be applicable to solar-type Protostars either.
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the alma pils survey first detections of ethylene oxide acetone and propanal toward the low mass protostar iras 16293 2422
arXiv: Solar and Stellar Astrophysics, 2016Co-Authors: J. M. Lykke, A Coutens, J K Jorgensen, Tyler L Bourke, R T Garrod, Holger S P Muller, P Bjerkeli, M H D Van Der Wiel, H CalcuttAbstract:One of the open questions in astrochemistry is how complex organic and prebiotic molecules are formed. Aims. Our aim is to start the process of compiling an inventory of oxygen-bearing complex organic molecules toward the solar-type Class 0 protostellar binary IRAS16293-2422 from an unbiased spectral survey with ALMA (PILS). Here we focus on the new detections of ethylene oxide (c-C$_2$H$_4$O), acetone (CH$_3$COCH$_3$), and propanal (C$_2$H$_5$CHO). Methods. With ALMA, we surveyed the spectral range from 329 to 363 GHz at 0.5$"$ (60 AU diameter) resolution. Using a simple model for the molecular emission in LTE, the excitation temperatures and column densities of each species were constrained. Results. We successfully detect propanal (44 lines), ethylene oxide (20 lines) and acetone (186 lines) toward one component of the protostellar binary, IRAS16293B. The high resolution maps demonstrate that the emission for all investigated species originates from the compact central region close to the protostar. This, along with a derived common excitation temperature of $\sim$ 125 K, is consistent with a coexistence of these molecules in the same gas. Conclusions. The observations mark the first detections of acetone, propanal and ethylene oxide toward a low-mass protostar. The relative abundance ratios of the two sets of isomers (CH$_3$COCH$_3$/C$_2$H$_5$CHO $\sim$ 8 and CH$_3$CHO/c-C$_2$H$_4$O $\sim$ 12) are comparable to previous observations toward high-mass Protostars. The majority of observed abundance ratios from these results as well as those measured toward high-mass Protostars are up to an order of magnitude above the predictions from chemical models. This may reflect either missing reactions or uncertain rates in the chemical networks. The physical conditions, such as temperatures or densities, used in the models, may not be applicable to solar-type Protostars either.
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probing the effects of external irradiation on low mass Protostars through unbiased line surveys
arXiv: Solar and Stellar Astrophysics, 2015Co-Authors: J K Jorgensen, Nami Sakai, Johan E Lindberg, Yoshimasa Watanabe, Suzanne E Bisschop, Satoshi YamamotoAbstract:(abridged) Context: The envelopes of molecular gas around embedded low-mass Protostars show different chemistries, which can be used to trace their formation history and physical conditions. The excitation of some molecular species can also be used to trace these physical conditions, making it possible to constrain e.g. sources of heating and excitation. Aims: To study the range of influence of an intermediate-mass Herbig Be protostar, and to find what chemical and physical impact feedback effects from the environment may have on embedded Protostars. Methods: We follow up on an earlier line survey of the Class 0/I source R CrA IRS7B in the 0.8 mm window with an unbiased line survey of the same source in the 1.3 mm window using the APEX telescope. We also study the excitation of the key species H2CO, CH3OH, and c-C3H2 in a complete sample of the 18 embedded Protostars in the Corona Australis star-forming region. Radiative transfer models are used to establish abundances of the molecular species. Results: We detect line emission from 20 molecular species (32 including isotopologues) in the two surveys. The most complex species detected are CH3OH, CH3CCH, CH3CHO, and CH3CN. Several complex organics are significantly under-abundant in comparison with "hot corino" Protostars. The H2CO temperatures of the sources in the region decrease with the distance to the Herbig Be star R CrA, whereas the c-C3H2 temperatures remain constant across the star-forming region. Conclusions: The high H2CO temperatures observed towards objects close to R CrA suggest that this star has a sphere of influence of several 10000 AU in which it increases the temperature of the molecular gas to 30-50 K through irradiation. The chemistry in the IRS7B envelope differs significantly from many other embedded Protostars, which could be an effect of the external irradiation from R CrA.
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a recent accretion burst in the low mass protostar iras 15398 3359 alma imaging of its related chemistry
The Astrophysical Journal, 2013Co-Authors: J K Jorgensen, R Visser, Nami Sakai, Edwin A Bergin, C Brinch, Daniel Harsono, Johan E Lindberg, Ewine F Van Dishoeck, Satoshi YamamotoAbstract:Low-mass Protostars have been suggested to show highly variable accretion rates throughout their evolution. Such changes in accretion, and related heating of their ambient envelopes, may trigger significant chemical variations on different spatial scales and from source-to-source. We present images of emission from C17O, H13CO+, CH3OH, C34S and C2H toward the low-mass protostar IRAS 15398-3359 on 0.''5 (75 AU diameter) scales with the Atacama Large Millimeter/submillimeter Array at 340 GHz. The resolved images show that the emission from H13CO+ is only present in a ring-like structure with a radius of about 1-1.''5 (150-200 AU) whereas the CO and other high dipole moment molecules are centrally condensed toward the location of the central protostar. We propose that HCO+ is destroyed by water vapor present on small scales. The origin of this water vapor is likely an accretion burst during the last 100-1000 yr increasing the luminosity of IRAS 15398-3359 by a factor of 100 above its current luminosity. Such a burst in luminosity can also explain the centrally condensed CH3OH and extended warm carbon-chain chemistry observed in this source and furthermore be reflected in the relative faintness of its compact continuum emission compared to other Protostars.
