C. Fallscheer - Academia.edu (original) (raw)

Papers by C. Fallscheer

Research paper thumbnail of A First Look at the Auriga-California Giant Molecular Cloud With Herschel and the Cso: Census of the Young Stellar Objects and the Dense Gas

The Astrophysical Journal, 2013

We have mapped the Auriga/California molecular cloud with the Herschel PACS and SPIRE cameras and... more We have mapped the Auriga/California molecular cloud with the Herschel PACS and SPIRE cameras and the Bolocam 1.1 mm camera on the Caltech Submillimeter Observatory (CSO) with the eventual goal of quantifying the star formation and cloud structure in this Giant Molecular Cloud (GMC) that is comparable in size and mass to the Orion GMC, but which appears to be forming far fewer stars. We have tabulated 60 compact 70/160 µm sources that are -2likely pre-main-sequence objects and correlated those with Spitzer and WISE mid-IR sources. At 1.1 mm we find 18 cold, compact sources and discuss their properties. The most important result from this part of our study is that we find a modest number of additional compact young objects beyond those identified at shorter wavelengths with Spitzer. We also describe the dust column density and temperature structure derived from our photometric maps. The column density peaks at a few × 10 22 cm −2 (N H2 ) and is distributed in a clear filamentary structure along which nearly all the pre-main-sequence objects are found. We compare the YSO surface density to the gas column density and find a strong non-linear correlation between them. The dust temperature in the densest parts of the filaments drops to ∼ 10K from values ∼ 14-15K in the low density parts of the cloud. We also derive the cumulative mass fraction and probability density function of material in the cloud which we compare with similar data on other star-forming clouds.

Research paper thumbnail of A High-Mass Dusty Disk Candidate: The Case of Iras 18151–1208

The Astrophysical Journal, 2011

Many questions remain regarding the properties of disks around massive prototstars. Here we prese... more Many questions remain regarding the properties of disks around massive prototstars. Here we present the observations of a high mass protostellar object including an elongated dust continuum structure perpendicular to the outflow. Submillimeter Array 230 GHz line and continuum observations of the high mass protostellar object IRAS 18151-1208 along with single dish IRAM 30 m observations afford us high spatial resolution (0.8 ′′ ) as well as recovery of the extended emission that gets filtered out by the interferometer. The observations of 12 CO confirm the outflow direction to be in the southeast-northwest direction, and the 1.3 mm continuum exhibits an elongation in the direction perpendicular to the outflow. We model the physical parameters of the elongated structure by simultaneously fitting the observed spectral energy distribution (SED) and the brightness profile along the major axis using the 3D Radiative Transfer code MC3D. Assuming a density profile similar to that of a low mass disk, we can also reproduce the observations of this high mass protostellar object. This is achieved by using the same density distribution and flaring parameters as were used in the low mass case, and scaling up the size parameters that successfully modeled the circumstellar disk of several T Tauri stars. We also calculate that a region within the inner 30 AU of such a high mass disk is stable under the Toomre criterion. While we do not rule out other scenarios, we show here that the observations in the high mass regime are consistent with a scaled up version of a low mass disk. Implications on high mass star formation are discussed.

Research paper thumbnail of Herschel Observations of the W3 GMC: Clues to the Formation of Clusters of High-Mass Stars

The Astrophysical Journal, 2013

The W3 GMC is a prime target for the study of the early stages of high-mass star formation. We ha... more The W3 GMC is a prime target for the study of the early stages of high-mass star formation. We have used Herschel data from the HOBYS key program to produce and analyze column density and temperature maps. Two preliminary catalogs were produced by extracting sources from the column density map and from Herschel maps convolved to the 500 µm resolution. Herschel reveals that among the compact sources (FWHM<0.45 pc), W3 East, W3 West, and W3 (OH) are the most massive and luminous and have the highest column density. Considering the unique properties of W3 East and W3 West, the only clumps with on-going high-mass star formation, we suggest a 'convergent constructive feedback' scenario to account for the formation of a cluster with decreasing age and increasing system/source mass toward the innermost regions. This process, which relies on feedback by high-mass stars to ensure the availability of material during cluster formation, could also lead to the creation of an environment suitable for the formation of Trapezium-like systems. In common with other scenarios proposed in other HOBYS studies, our results indicate that an active/dynamic process aiding in the accumulation, compression, and confinement of material is a critical feature of the high-mass star/cluster formation, distinguishing it from classical low-mass star formation. The environmental conditions and availability of triggers determine the form in which this process occurs, implying that high-mass star/cluster formation could arise from a range of scenarios: from large scale convergence of turbulent flows, to convergent constructive feedback or mergers of filaments.

Research paper thumbnail of Recent star formation in the Lupus clouds as seen by Herschel

Astronomy & Astrophysics, 2013

We present a study of the star formation histories of the Lupus I, III, and IV clouds using the H... more We present a study of the star formation histories of the Lupus I, III, and IV clouds using the Herschel 70-500 µm maps obtained by the Herschel Gould Belt Survey Key Project. By combining the new Herschel data with the existing Spitzer catalog we obtained an unprecedented census of prestellar sources and young stellar objects in the Lupus clouds, which allowed us to study the overall star formation rate (SFR) and efficiency (SFE). The high SFE of Lupus III, its decreasing SFR, and its large number of pre-main sequence stars with respect to proto-and prestellar sources, suggest that Lupus III is the most evolved cloud, and after having experienced a major star formation event in the past, is now approaching the end of its current star-forming cycle. Lupus I is currently undergoing a large star formation event, apparent by the increasing SFR, the large number of prestellar objects with respect to more evolved objects, and the high percentage of material at high extinction (e.g., above A V ≈ 8 mag). Also Lupus IV has an increasing SFR; however, the relative number of prestellar sources is much lower, suggesting that its star formation has not yet reached its peak.

Research paper thumbnail of Dissecting a hot molecular core: the case of G31.41+0.31

Astronomy & Astrophysics, 2011

ABSTRACT

Research paper thumbnail of Herschel observations of a potential core-forming clump: Perseus B1-E

Astronomy & Astrophysics, 2012

We present continuum observations of the Perseus B1-E region from the Herschel Gould Belt Survey.... more We present continuum observations of the Perseus B1-E region from the Herschel Gould Belt Survey. These Herschel data reveal a loose grouping of substructures at 160 − 500 µm not seen in previous submillimetre observations. We measure temperature and column density from these data and select the nine densest and coolest substructures for follow-up spectral line observations with the Green Bank Telescope. We find that the B1-E clump has a mass of ∼ 100 M ⊙ and appears to be gravitationally bound. Furthermore, of the nine substructures examined here, one substructure (B1-E2) appears to be itself bound. The substructures are typically less than a Jeans length from their nearest neighbour and thus, may interact on a timescale of ∼ 1 Myr. We propose that B1-E may be forming a first generation of dense cores, which could provide important constraints on the initial conditions of prestellar core formation. Our results suggest that B1-E may be influenced by a strong, localized magnetic field, but further observations are still required.

Research paper thumbnail of Rotational structure and outflow in the infrared dark cloud 18223-3

Astronomy and Astrophysics, 2009

ABSTRACT

Research paper thumbnail of Different evolutionary stages in massive star formation

Astronomy & Astrophysics, 2013

Aims: Massive stars form in clusters, and they are often found in different evolutionary stages l... more Aims: Massive stars form in clusters, and they are often found in different evolutionary stages located close to each other. To understand evolutionary and environmental effects during the formation of high-mass stars, we observed three regions of massive star formation at different evolutionary stages, and all are found that in the same natal molecular cloud. Methods: The three regions, S255IR,

Research paper thumbnail of Molecular outflows and hot molecular cores in G24.78+0.08 at sub-arcsecond angular resolution

Astronomy & Astrophysics, 2011

Context. This study is part of a large project to study the physics of accretion and molecular ou... more Context. This study is part of a large project to study the physics of accretion and molecular outflows towards a selected sample of high-mass star-forming regions that show evidence of infall and rotation from previous studies. Aims: We wish to make a thorough study at high-angular resolution of the structure and kinematics of the HMCs and corresponding molecular outflows in the high-mass star-forming region G24.78+0.08. Methods: We carried out SMA and IRAM PdBI observations at 1.3 and 1.4 mm, respectively, of dust and of typical high-density and molecular outflow tracers with resolutions of < 1". Complementary IRAM 30-m 12CO and 13CO observations were carried out to recover the short spacing information of the molecular outflows. Results: The millimeter continuum emission towards cores G24 A1 and A2 has been resolved into three and two cores, respectively, and named A1, A1b, A1c, A2, and A2b. All these cores are aligned in a southeast-northwest direction coincident with that of the molecular outflows detected in the region, which suggests a preferential direction for star formation in this region. The masses of the cores range from 7 to 22 M&sun;, and the rotational temperatures from 128 to 180 K. The high-density tracers have revealed the existence of two velocity components towards A1. One of them peaks close to the position of the millimeter continuum peak and of the HC Hii region and is associated with the velocity gradient seen in CH3CN towards this core, while the other one peaks southwest of core A1 and is not associated with any millimeter continuum emission peak. The position-velocity plots along outflow A and the 13CO (2-1) averaged blueshifted and redshifted emission indicate that this outflow is driven by core A2. Core A1 apparently does not drive any outflow. The knotty appearance of the highly collimated outflow C and the 12CO position-velocity plot suggest an episodic outflow, where the knots are made of swept-up ambient gas.

Research paper thumbnail of The Herschel view of the on-going star formation in the Vela-C molecular cloud

Astronomy & Astrophysics, 2012

Aims. As part of the Herschel guaranteed time key program 'HOBYS', we present the PACS and SPIRE ... more Aims. As part of the Herschel guaranteed time key program 'HOBYS', we present the PACS and SPIRE photometric survey of the star forming region Vela-C, one of the nearest sites of low-to-high-mass star formation in the Galactic plane. Our main objectives are to take a census of the cold sources and to derive their mass distribution down to a few solar masses. Methods. Vela-C has been observed with PACS and SPIRE in parallel mode at five wavelengths between 70 µm and 500 µm over an area of about 3 square degrees. A photometric catalogue has been extracted from the detections in each of the five bands, using a threshold of 5 σ over the local background. Out of this catalogue we have selected a robust sub-sample of 268 sources, of which ∼ 75% are cloud clumps (diameter between 0.05 pc and 0.13 pc) and 25% are cores (diameter between 0.025 pc and 0.05 pc). Their Spectral Energy Distributions (SEDs) have been fitted with a modified black body function. We classify 48 sources as protostellar, based on their detection at 70 µm or at shorther wavelengths, and 218 as starless, because of non-detections at 70 µm. For two further sources, we do not provide a secure classification, but suggest they are Class 0 protostars. Results. From SED fitting we have derived key physical parameters (i.e. mass, temperature, bolometric luminosity). Protostellar sources are in general warmer ( T =12.8 K) and more compact ( diameter =0.040 pc) than starless sources ( T =10.3 K, diameter =0.067 pc). Both these evidences can be ascribed to the presence of an internal source(s) of moderate heating, which also causes a temperature gradient and hence a more peaked intensity distribution. Moreover, the reduced dimensions of protostellar sources may indicate that they will not fragment further. A virial analysis of the starless sources gives an upper limit of 90% for the sources gravitationally bound and therefore prestellar in nature. A luminosity vs. mass diagram of the two populations shows that protostellar sources are in the early accretion phase, while prestellar sources populate a region of the diagram where mass accretion has not started yet. We fit a power law N(logM) ∝ M −1.1±0.2 to the linear portion of the mass distribution of prestellar sources. This is in between that typical of CO clumps and those of cores in nearby star-forming regions. We interpret this as a result of the inhomogeneity of our sample, which is composed of comparable fractions of clumps and cores.

Research paper thumbnail of Cluster-formation in the Rosette molecular cloud at the junctions of filaments

Astronomy & Astrophysics, 2012

Aims. For many years feedback processes generated by OB-stars in molecular clouds, including expa... more Aims. For many years feedback processes generated by OB-stars in molecular clouds, including expanding ionization fronts, stellar winds, or UV-radiation, have been proposed to trigger subsequent star formation. However, hydrodynamic models including radiation and gravity show that UV-illumination has little or no impact on the global dynamical evolution of the cloud. Instead, gravitational collapse of filaments and/or merging of filamentary structures can lead to building up dense high-mass star-forming clumps. However, the overall density structure of the cloud has a large influence on this process, and requires a better understanding. Methods. The Rosette molecular cloud, irradiated by the NGC 2244 cluster, is a template region for triggered star-formation, and we investigated its spatial and density structure by applying a curvelet analysis, a filament-tracing algorithm (DisPerSE), and probability density functions (PDFs) on Herschel ⋆ column density maps, obtained within the HOBYS key program.

Research paper thumbnail of A Herschel and BIMA study of the sequential star formation near the W 48A H II region

Monthly Notices of the Royal Astronomical Society, 2014

We present the results of Herschel HOBYS photometric mapping combined with BIMA observations and ... more We present the results of Herschel HOBYS photometric mapping combined with BIMA observations and additional archival data, and perform an in-depth study of the evolutionary phases of the star-forming clumps in W 48A and their surroundings. Age estimates for the compact sources were derived from bolometric luminosities and envelope masses, which were obtained from the dust continuum emission, and agree within an order of magnitude with age estimates from molecular line and radio data. The clumps in W 48A are linearly aligned by age (east-old to west-young): we find a UC Hii region, a young stellar object (YSO) with class II methanol maser emission, a YSO with a massive outflow, and finally the NH 2 D prestellar cores from Pillai et al. This remarkable positioning reflects the (star) formation history of the region. We find that it is unlikely that the star formation in the W 48A molecular cloud was triggered by the UC Hii region and discuss the Aquila supershell expansion as a mayor influence on the evolution of W 48A. We conclude that the combination of Herschel continuum data with interferometric molecular line and radio continuum data is important to derive trustworthy age estimates and interpret the origin of large scale structures through kinematic information.

Research paper thumbnail of A First Look at the Auriga-California Giant Molecular Cloud With Herschel and the Cso: Census of the Young Stellar Objects and the Dense Gas

The Astrophysical Journal, 2013

We have mapped the Auriga/California molecular cloud with the Herschel PACS and SPIRE cameras and... more We have mapped the Auriga/California molecular cloud with the Herschel PACS and SPIRE cameras and the Bolocam 1.1 mm camera on the Caltech Submillimeter Observatory (CSO) with the eventual goal of quantifying the star formation and cloud structure in this Giant Molecular Cloud (GMC) that is comparable in size and mass to the Orion GMC, but which appears to be forming far fewer stars. We have tabulated 60 compact 70/160 µm sources that are -2likely pre-main-sequence objects and correlated those with Spitzer and WISE mid-IR sources. At 1.1 mm we find 18 cold, compact sources and discuss their properties. The most important result from this part of our study is that we find a modest number of additional compact young objects beyond those identified at shorter wavelengths with Spitzer. We also describe the dust column density and temperature structure derived from our photometric maps. The column density peaks at a few × 10 22 cm −2 (N H2 ) and is distributed in a clear filamentary structure along which nearly all the pre-main-sequence objects are found. We compare the YSO surface density to the gas column density and find a strong non-linear correlation between them. The dust temperature in the densest parts of the filaments drops to ∼ 10K from values ∼ 14-15K in the low density parts of the cloud. We also derive the cumulative mass fraction and probability density function of material in the cloud which we compare with similar data on other star-forming clouds.

Research paper thumbnail of A High-Mass Dusty Disk Candidate: The Case of Iras 18151–1208

The Astrophysical Journal, 2011

Many questions remain regarding the properties of disks around massive prototstars. Here we prese... more Many questions remain regarding the properties of disks around massive prototstars. Here we present the observations of a high mass protostellar object including an elongated dust continuum structure perpendicular to the outflow. Submillimeter Array 230 GHz line and continuum observations of the high mass protostellar object IRAS 18151-1208 along with single dish IRAM 30 m observations afford us high spatial resolution (0.8 ′′ ) as well as recovery of the extended emission that gets filtered out by the interferometer. The observations of 12 CO confirm the outflow direction to be in the southeast-northwest direction, and the 1.3 mm continuum exhibits an elongation in the direction perpendicular to the outflow. We model the physical parameters of the elongated structure by simultaneously fitting the observed spectral energy distribution (SED) and the brightness profile along the major axis using the 3D Radiative Transfer code MC3D. Assuming a density profile similar to that of a low mass disk, we can also reproduce the observations of this high mass protostellar object. This is achieved by using the same density distribution and flaring parameters as were used in the low mass case, and scaling up the size parameters that successfully modeled the circumstellar disk of several T Tauri stars. We also calculate that a region within the inner 30 AU of such a high mass disk is stable under the Toomre criterion. While we do not rule out other scenarios, we show here that the observations in the high mass regime are consistent with a scaled up version of a low mass disk. Implications on high mass star formation are discussed.

Research paper thumbnail of Herschel Observations of the W3 GMC: Clues to the Formation of Clusters of High-Mass Stars

The Astrophysical Journal, 2013

The W3 GMC is a prime target for the study of the early stages of high-mass star formation. We ha... more The W3 GMC is a prime target for the study of the early stages of high-mass star formation. We have used Herschel data from the HOBYS key program to produce and analyze column density and temperature maps. Two preliminary catalogs were produced by extracting sources from the column density map and from Herschel maps convolved to the 500 µm resolution. Herschel reveals that among the compact sources (FWHM<0.45 pc), W3 East, W3 West, and W3 (OH) are the most massive and luminous and have the highest column density. Considering the unique properties of W3 East and W3 West, the only clumps with on-going high-mass star formation, we suggest a 'convergent constructive feedback' scenario to account for the formation of a cluster with decreasing age and increasing system/source mass toward the innermost regions. This process, which relies on feedback by high-mass stars to ensure the availability of material during cluster formation, could also lead to the creation of an environment suitable for the formation of Trapezium-like systems. In common with other scenarios proposed in other HOBYS studies, our results indicate that an active/dynamic process aiding in the accumulation, compression, and confinement of material is a critical feature of the high-mass star/cluster formation, distinguishing it from classical low-mass star formation. The environmental conditions and availability of triggers determine the form in which this process occurs, implying that high-mass star/cluster formation could arise from a range of scenarios: from large scale convergence of turbulent flows, to convergent constructive feedback or mergers of filaments.

Research paper thumbnail of Recent star formation in the Lupus clouds as seen by Herschel

Astronomy & Astrophysics, 2013

We present a study of the star formation histories of the Lupus I, III, and IV clouds using the H... more We present a study of the star formation histories of the Lupus I, III, and IV clouds using the Herschel 70-500 µm maps obtained by the Herschel Gould Belt Survey Key Project. By combining the new Herschel data with the existing Spitzer catalog we obtained an unprecedented census of prestellar sources and young stellar objects in the Lupus clouds, which allowed us to study the overall star formation rate (SFR) and efficiency (SFE). The high SFE of Lupus III, its decreasing SFR, and its large number of pre-main sequence stars with respect to proto-and prestellar sources, suggest that Lupus III is the most evolved cloud, and after having experienced a major star formation event in the past, is now approaching the end of its current star-forming cycle. Lupus I is currently undergoing a large star formation event, apparent by the increasing SFR, the large number of prestellar objects with respect to more evolved objects, and the high percentage of material at high extinction (e.g., above A V ≈ 8 mag). Also Lupus IV has an increasing SFR; however, the relative number of prestellar sources is much lower, suggesting that its star formation has not yet reached its peak.

Research paper thumbnail of Dissecting a hot molecular core: the case of G31.41+0.31

Astronomy & Astrophysics, 2011

ABSTRACT

Research paper thumbnail of Herschel observations of a potential core-forming clump: Perseus B1-E

Astronomy & Astrophysics, 2012

We present continuum observations of the Perseus B1-E region from the Herschel Gould Belt Survey.... more We present continuum observations of the Perseus B1-E region from the Herschel Gould Belt Survey. These Herschel data reveal a loose grouping of substructures at 160 − 500 µm not seen in previous submillimetre observations. We measure temperature and column density from these data and select the nine densest and coolest substructures for follow-up spectral line observations with the Green Bank Telescope. We find that the B1-E clump has a mass of ∼ 100 M ⊙ and appears to be gravitationally bound. Furthermore, of the nine substructures examined here, one substructure (B1-E2) appears to be itself bound. The substructures are typically less than a Jeans length from their nearest neighbour and thus, may interact on a timescale of ∼ 1 Myr. We propose that B1-E may be forming a first generation of dense cores, which could provide important constraints on the initial conditions of prestellar core formation. Our results suggest that B1-E may be influenced by a strong, localized magnetic field, but further observations are still required.

Research paper thumbnail of Rotational structure and outflow in the infrared dark cloud 18223-3

Astronomy and Astrophysics, 2009

ABSTRACT

Research paper thumbnail of Different evolutionary stages in massive star formation

Astronomy & Astrophysics, 2013

Aims: Massive stars form in clusters, and they are often found in different evolutionary stages l... more Aims: Massive stars form in clusters, and they are often found in different evolutionary stages located close to each other. To understand evolutionary and environmental effects during the formation of high-mass stars, we observed three regions of massive star formation at different evolutionary stages, and all are found that in the same natal molecular cloud. Methods: The three regions, S255IR,

Research paper thumbnail of Molecular outflows and hot molecular cores in G24.78+0.08 at sub-arcsecond angular resolution

Astronomy & Astrophysics, 2011

Context. This study is part of a large project to study the physics of accretion and molecular ou... more Context. This study is part of a large project to study the physics of accretion and molecular outflows towards a selected sample of high-mass star-forming regions that show evidence of infall and rotation from previous studies. Aims: We wish to make a thorough study at high-angular resolution of the structure and kinematics of the HMCs and corresponding molecular outflows in the high-mass star-forming region G24.78+0.08. Methods: We carried out SMA and IRAM PdBI observations at 1.3 and 1.4 mm, respectively, of dust and of typical high-density and molecular outflow tracers with resolutions of < 1". Complementary IRAM 30-m 12CO and 13CO observations were carried out to recover the short spacing information of the molecular outflows. Results: The millimeter continuum emission towards cores G24 A1 and A2 has been resolved into three and two cores, respectively, and named A1, A1b, A1c, A2, and A2b. All these cores are aligned in a southeast-northwest direction coincident with that of the molecular outflows detected in the region, which suggests a preferential direction for star formation in this region. The masses of the cores range from 7 to 22 M&sun;, and the rotational temperatures from 128 to 180 K. The high-density tracers have revealed the existence of two velocity components towards A1. One of them peaks close to the position of the millimeter continuum peak and of the HC Hii region and is associated with the velocity gradient seen in CH3CN towards this core, while the other one peaks southwest of core A1 and is not associated with any millimeter continuum emission peak. The position-velocity plots along outflow A and the 13CO (2-1) averaged blueshifted and redshifted emission indicate that this outflow is driven by core A2. Core A1 apparently does not drive any outflow. The knotty appearance of the highly collimated outflow C and the 12CO position-velocity plot suggest an episodic outflow, where the knots are made of swept-up ambient gas.

Research paper thumbnail of The Herschel view of the on-going star formation in the Vela-C molecular cloud

Astronomy & Astrophysics, 2012

Aims. As part of the Herschel guaranteed time key program 'HOBYS', we present the PACS and SPIRE ... more Aims. As part of the Herschel guaranteed time key program 'HOBYS', we present the PACS and SPIRE photometric survey of the star forming region Vela-C, one of the nearest sites of low-to-high-mass star formation in the Galactic plane. Our main objectives are to take a census of the cold sources and to derive their mass distribution down to a few solar masses. Methods. Vela-C has been observed with PACS and SPIRE in parallel mode at five wavelengths between 70 µm and 500 µm over an area of about 3 square degrees. A photometric catalogue has been extracted from the detections in each of the five bands, using a threshold of 5 σ over the local background. Out of this catalogue we have selected a robust sub-sample of 268 sources, of which ∼ 75% are cloud clumps (diameter between 0.05 pc and 0.13 pc) and 25% are cores (diameter between 0.025 pc and 0.05 pc). Their Spectral Energy Distributions (SEDs) have been fitted with a modified black body function. We classify 48 sources as protostellar, based on their detection at 70 µm or at shorther wavelengths, and 218 as starless, because of non-detections at 70 µm. For two further sources, we do not provide a secure classification, but suggest they are Class 0 protostars. Results. From SED fitting we have derived key physical parameters (i.e. mass, temperature, bolometric luminosity). Protostellar sources are in general warmer ( T =12.8 K) and more compact ( diameter =0.040 pc) than starless sources ( T =10.3 K, diameter =0.067 pc). Both these evidences can be ascribed to the presence of an internal source(s) of moderate heating, which also causes a temperature gradient and hence a more peaked intensity distribution. Moreover, the reduced dimensions of protostellar sources may indicate that they will not fragment further. A virial analysis of the starless sources gives an upper limit of 90% for the sources gravitationally bound and therefore prestellar in nature. A luminosity vs. mass diagram of the two populations shows that protostellar sources are in the early accretion phase, while prestellar sources populate a region of the diagram where mass accretion has not started yet. We fit a power law N(logM) ∝ M −1.1±0.2 to the linear portion of the mass distribution of prestellar sources. This is in between that typical of CO clumps and those of cores in nearby star-forming regions. We interpret this as a result of the inhomogeneity of our sample, which is composed of comparable fractions of clumps and cores.

Research paper thumbnail of Cluster-formation in the Rosette molecular cloud at the junctions of filaments

Astronomy & Astrophysics, 2012

Aims. For many years feedback processes generated by OB-stars in molecular clouds, including expa... more Aims. For many years feedback processes generated by OB-stars in molecular clouds, including expanding ionization fronts, stellar winds, or UV-radiation, have been proposed to trigger subsequent star formation. However, hydrodynamic models including radiation and gravity show that UV-illumination has little or no impact on the global dynamical evolution of the cloud. Instead, gravitational collapse of filaments and/or merging of filamentary structures can lead to building up dense high-mass star-forming clumps. However, the overall density structure of the cloud has a large influence on this process, and requires a better understanding. Methods. The Rosette molecular cloud, irradiated by the NGC 2244 cluster, is a template region for triggered star-formation, and we investigated its spatial and density structure by applying a curvelet analysis, a filament-tracing algorithm (DisPerSE), and probability density functions (PDFs) on Herschel ⋆ column density maps, obtained within the HOBYS key program.

Research paper thumbnail of A Herschel and BIMA study of the sequential star formation near the W 48A H II region

Monthly Notices of the Royal Astronomical Society, 2014

We present the results of Herschel HOBYS photometric mapping combined with BIMA observations and ... more We present the results of Herschel HOBYS photometric mapping combined with BIMA observations and additional archival data, and perform an in-depth study of the evolutionary phases of the star-forming clumps in W 48A and their surroundings. Age estimates for the compact sources were derived from bolometric luminosities and envelope masses, which were obtained from the dust continuum emission, and agree within an order of magnitude with age estimates from molecular line and radio data. The clumps in W 48A are linearly aligned by age (east-old to west-young): we find a UC Hii region, a young stellar object (YSO) with class II methanol maser emission, a YSO with a massive outflow, and finally the NH 2 D prestellar cores from Pillai et al. This remarkable positioning reflects the (star) formation history of the region. We find that it is unlikely that the star formation in the W 48A molecular cloud was triggered by the UC Hii region and discuss the Aquila supershell expansion as a mayor influence on the evolution of W 48A. We conclude that the combination of Herschel continuum data with interferometric molecular line and radio continuum data is important to derive trustworthy age estimates and interpret the origin of large scale structures through kinematic information.