11 research outputs found
Herschel Gould Belt Survey Observations of Dense Cores in the Cepheus Flare Clouds
We present Herschel SPIRE and PACS maps of the Cepheus Flare clouds L1157, L1172, L1228, L1241, and L1251, observed by the Herschel Gould Belt Survey of nearby star-forming molecular clouds. Through modified blackbody fits to the SPIRE and PACS data, we determine typical cloud column densities of (0.5â1.0) Ă 1021 cmâ2 and typical cloud temperatures of 14â15 K. Using the getsources identification algorithm, we extract 832 dense cores from the SPIRE and PACS data at 160â500 ÎŒm. From placement in a mass versus size diagram, we consider 303 to be candidate prestellar cores, and 178 of these to be "robust" prestellar cores. From an independent extraction of sources at 70 ÎŒm, we consider 25 of the 832 dense cores to be protostellar. The distribution of background column densities coincident with candidate prestellar cores peaks at (2â4) Ă 1021 cmâ2. About half of the candidate prestellar cores in Cepheus may have formed as a result of the widespread fragmentation expected to occur within filaments of "transcritical" line mass. The lognormal robust prestellar core mass function (CMF) drawn from all five Cepheus clouds peaks at 0.56 Mâ and has a width of âŒ0.5 dex, similar to that of Aquila's CMF. Indeed, the width of Cepheus's aggregate CMF is similar to the stellar system initial mass function (IMF). The similarity of CMF widths in different clouds and the system IMF suggests a common, possibly turbulent origin for seeding the fluctuations that evolve into prestellar cores and stars
Herschel Gould Belt Survey Observations of Dense Cores in the Cepheus Flare Clouds
Abstract: We present Herschel SPIRE and PACS maps of the Cepheus Flare clouds L1157, L1172, L1228, L1241, and L1251, observed by the Herschel Gould Belt Survey of nearby star-forming molecular clouds. Through modified blackbody fits to the SPIRE and PACS data, we determine typical cloud column densities of (0.5â1.0) Ă 1021 cmâ2 and typical cloud temperatures of 14â15 K. Using the getsources identification algorithm, we extract 832 dense cores from the SPIRE and PACS data at 160â500 ÎŒm. From placement in a mass versus size diagram, we consider 303 to be candidate prestellar cores, and 178 of these to be ârobustâ prestellar cores. From an independent extraction of sources at 70 ÎŒm, we consider 25 of the 832 dense cores to be protostellar. The distribution of background column densities coincident with candidate prestellar cores peaks at (2â4) Ă 1021 cmâ2. About half of the candidate prestellar cores in Cepheus may have formed as a result of the widespread fragmentation expected to occur within filaments of âtranscriticalâ line mass. The lognormal robust prestellar core mass function (CMF) drawn from all five Cepheus clouds peaks at 0.56 Mâ and has a width of âŒ0.5 dex, similar to that of Aquilaâs CMF. Indeed, the width of Cepheusâs aggregate CMF is similar to the stellar system initial mass function (IMF). The similarity of CMF widths in different clouds and the system IMF suggests a common, possibly turbulent origin for seeding the fluctuations that evolve into prestellar cores and stars
Multi-scale study of protostellar dense core formation inside interstellar filaments
Des nuages molĂ©culaires aux Ă©toiles, l'ensemble des stades d'Ă©volution des Ă©toiles jeunes peuvent ĂȘtre observĂ©s dans le domaine submillimĂ©trique. A cette fin, le tĂ©lescope Herschel a observĂ©, dans le cadre d'un relevĂ© de la Ceinture de Gould, plusieurs nuages molĂ©culaires. Lorsque ces nuages se fragmentent, des coeurs denses, accumulant de la poussiĂšre et du gaz, se forment et se contractent. Nous avons effectuĂ© un relevĂ© exhaustif des coeurs denses prĂ©stellaires dans le nuage molĂ©culaire d'Ophiuchus qui apparaissent couplĂ©s avec des structures filamentaires dans le cadre du paradigme de la formation d'Ă©toiles au sein de filaments interstellaires. La rĂ©gion n'Ă©tait pas connue pour ĂȘtre filamentaire, malgrĂ© des alignements de protoĂ©toiles observables. Ce nuage molĂ©culaire prĂ©sente la particularitĂ© d'ĂȘtre soumis Ă une rĂ©troaction importante venant d'Ă©toiles actives Ă proximitĂ©, visible dans la structure du nuage molĂ©culaire. Oph B-11, mise en Ă©vidence par des observations interfĂ©romĂ©triques, est un prĂ©curseur de naine brune, de masse finale trop faible pour que l'Ă©toile produite brĂ»le de l'hydrogĂšne. Leur mĂ©canisme de formation est mal connu. Il faut caractĂ©riser et observer un premier candidat prĂ©-naine brune. Oph B-11 a Ă©tĂ© dĂ©tectĂ©e Ă proximitĂ© d'un choc proche, que nous avons caractĂ©risĂ© chimiquement. De plus, Ă plus haute rĂ©solution avec ALMA, nous avons montrĂ© l'environnement molĂ©culaire structurĂ©, contraint le mĂ©canisme de formation de ce type d'objet. Ces observations dĂ©voilent une sĂ©rie de chocs dans plusieurs traceurs, coĂŻncidant avec la dĂ©tection de la prĂ©-naine brune, favorisant le scĂ©nario gravo-turbulent pour la formation des naines brunes.From molecular clouds to stars, every step of the evolution of young stars can be observed in the submillimetric range. The Herschel Space Telescope observed, as part of the Herschel Gould Belt Survey, many molecular clouds.When these molecular clouds are fragmenting, dense prestellar cores accumulating dust and gaz are forming and contracting. We performed a census of prestellar dense cores in the Ophiuchus Molecular Cloud, which appear to be coupled with filamentary structures, as part of the paradigm of star-formation inside insterstellar filaments. The region was not previously known as filamentary, despite the observation of protostellar alignments.This molecular could is under the heavy feedback of active stars nearby seen in the structure of the molecular cloud.Oph B-11, detected with interferometric observations, is a brown dwarf precursor, which final mass will not be important enough for the final star to burn hydrogen. Their formation mechanism is not well constrained, we must find and characterize a first candidate pre-brown dwarf.Oph B-11 was detected along a nearby shock, we characterize chemically. Moreover, higher resolution studies with ALMA show a structured molecular environment, and help us constrain the mechanism of formation of this kind of objects. These observations show a series of shocks in differents tracers, spatially coincident with the detected position of the pre-brown dwarf, in favor of the gravo-turbulent scenario for the formation of brown dwarfs
Etude multi-Ă©chelle de la formation des coeurs denses protostellaires au sein des filaments interstellaires
From molecular clouds to stars, every step of the evolution of young stars can be observed in the submillimetric range. The Herschel Space Telescope observed, as part of the Herschel Gould Belt Survey, many molecular clouds.When these molecular clouds are fragmenting, dense prestellar cores accumulating dust and gaz are forming and contracting. We performed a census of prestellar dense cores in the Ophiuchus Molecular Cloud, which appear to be coupled with filamentary structures, as part of the paradigm of star-formation inside insterstellar filaments. The region was not previously known as filamentary, despite the observation of protostellar alignments.This molecular could is under the heavy feedback of active stars nearby seen in the structure of the molecular cloud.Oph B-11, detected with interferometric observations, is a brown dwarf precursor, which final mass will not be important enough for the final star to burn hydrogen. Their formation mechanism is not well constrained, we must find and characterize a first candidate pre-brown dwarf.Oph B-11 was detected along a nearby shock, we characterize chemically. Moreover, higher resolution studies with ALMA show a structured molecular environment, and help us constrain the mechanism of formation of this kind of objects. These observations show a series of shocks in differents tracers, spatially coincident with the detected position of the pre-brown dwarf, in favor of the gravo-turbulent scenario for the formation of brown dwarfs.Des nuages molĂ©culaires aux Ă©toiles, l'ensemble des stades d'Ă©volution des Ă©toiles jeunes peuvent ĂȘtre observĂ©s dans le domaine submillimĂ©trique. A cette fin, le tĂ©lescope Herschel a observĂ©, dans le cadre d'un relevĂ© de la Ceinture de Gould, plusieurs nuages molĂ©culaires. Lorsque ces nuages se fragmentent, des coeurs denses, accumulant de la poussiĂšre et du gaz, se forment et se contractent. Nous avons effectuĂ© un relevĂ© exhaustif des coeurs denses prĂ©stellaires dans le nuage molĂ©culaire d'Ophiuchus qui apparaissent couplĂ©s avec des structures filamentaires dans le cadre du paradigme de la formation d'Ă©toiles au sein de filaments interstellaires. La rĂ©gion n'Ă©tait pas connue pour ĂȘtre filamentaire, malgrĂ© des alignements de protoĂ©toiles observables. Ce nuage molĂ©culaire prĂ©sente la particularitĂ© d'ĂȘtre soumis Ă une rĂ©troaction importante venant d'Ă©toiles actives Ă proximitĂ©, visible dans la structure du nuage molĂ©culaire. Oph B-11, mise en Ă©vidence par des observations interfĂ©romĂ©triques, est un prĂ©curseur de naine brune, de masse finale trop faible pour que l'Ă©toile produite brĂ»le de l'hydrogĂšne. Leur mĂ©canisme de formation est mal connu. Il faut caractĂ©riser et observer un premier candidat prĂ©-naine brune. Oph B-11 a Ă©tĂ© dĂ©tectĂ©e Ă proximitĂ© d'un choc proche, que nous avons caractĂ©risĂ© chimiquement. De plus, Ă plus haute rĂ©solution avec ALMA, nous avons montrĂ© l'environnement molĂ©culaire structurĂ©, contraint le mĂ©canisme de formation de ce type d'objet. Ces observations dĂ©voilent une sĂ©rie de chocs dans plusieurs traceurs, coĂŻncidant avec la dĂ©tection de la prĂ©-naine brune, favorisant le scĂ©nario gravo-turbulent pour la formation des naines brunes
Dust evolution in pre-stellar cores
International audienceDust grains are the building blocks of future planets. They evolve in size, shape and composition during the life cycle of the interstellar medium. We seek to understand the process which leads from diffuse medium grains to dust grains in the vicinity of protostars inside disks. As a first step, we propose to characterize the dust evolution inside pre-stellar cores thanks to multi-wavelength observations. We will present how NIKA2 maps are crucial to better constrain dust properties and we will introduce SIGMA: a new flexible dust model in open access
Dust evolution in pre-stellar cores
Dust grains are the building blocks of future planets. They evolve in size, shape and composition during the life cycle of the interstellar medium. We seek to understand the process which leads from diffuse medium grains to dust grains in the vicinity of protostars inside disks. As a first step, we propose to characterize the dust evolution inside pre-stellar cores thanks to multi-wavelength observations. We will present how NIKA2 maps are crucial to better constrain dust properties and we will introduce SIGMA: a new flexible dust model in open access
Millimetric thermal emission from the two faces of Iapetus
International audienceWe observed the two faces of Iapetus at 1.2and2.0mm using the New IRAM (Institut de RadioAstronomie MillimĂ©trique) Kids Array (NIKA2)mounted on the IRAM-30 m telescope. On Iapetusâ trailing side, we confirm thepredictionof Ries (2012). On the leading side, however, we find that thebrightnesstemperatureis much lower at 1.2 and 2.0 mm than observed at 3 mm by Ries (2012)
Probing the subsurface of the two faces of Iapetus
Saturnâs moon Iapetus, which is in synchronous rotation, is covered by an optically dark material mainly on its leading side, while its trailing side is significantly brighter. Because longer wavelengths probe deeper into the subsurface, observing both sides at a variety of wavelengths brings to light possible changes in thermal, compositional, and physical properties with depth. We have observed Iapetusâs leading and trailing hemispheres at 1.2 and 2.0 mm, using the NIKA2 camera mounted on the IRAM 30-m telescope, and compared our observations to others performed at mm to cm wavelengths. We calibrate our observations on Titan, which is simultaneously observed within the field of view. Due to the proximity of Saturn, it is sometimes difficult to separate Iapetusâs and Titanâs flux from that of Saturn, detected in the telescopeâs side lobes. Preliminary results show that the trailing hemisphere brightness temperatures at the two wavelengths are equal within error bars, unlike the prediction made by Ries (2012)[1]. On the leading side, we report a steep spectral slope of increasing brightness temperature (by 10 K) from 1.2 to 2.0 mm, which may indicate rapidly varying emissivities within the top few centimeters of the surface. Comparison to a diffuse scattering model and a thermal model will be necessary to further constrain the thermophysical properties of the subsurface of Iapetusâs two faces
The structure and characteristic scales of molecular clouds
The structure of molecular clouds holds important clues regarding the physical processes that lead to their formation and subsequent dynamical evolution. While it is well established that turbulence imprints a self-similar structure onto the clouds, other processes, such as gravity and stellar feedback, can break their scale-free nature. The break of self-similarity can manifest itself in the existence of characteristic scales that stand out from the underlying structure generated by turbulent motions. In this work, we investigate the structure of the Cygnus-X North and Polaris Flare molecular clouds, which represent two extremes in terms of their star formation activity. We characterize the structure of the clouds using the delta-variance (Î-variance) spectrum. In the Polaris Flare, the structure of the cloud is self-similar over more than one order of magnitude in spatial scales. In contrast, the Î-variance spectrum of Cygnus-X North exhibits an excess and a plateau on physical scales of â0.5â1.2 pc. In order to explain the observations for Cygnus-X North, we use synthetic maps where we overlay populations of discrete structures on top of a fractal Brownian motion (fBm) image. The properties of these structures, such as their major axis sizes, aspect ratios, and column density contrasts with the fBm image, are randomly drawn from parameterized distribution functions. We are able to show that, under plausible assumptions, it is possible to reproduce a Î-variance spectrum that resembles that of the Cygnus-X North region. We also use a âreverse engineeringâ approach in which we extract the compact structures in the Cygnus-X North cloud and reinject them onto an fBm map. Using this approach, the calculated Î-variance spectrum deviates from the observations and is an indication that the range of characteristic scales (â0.5â1.2 pc) observed in Cygnus-X North is not only due to the existence of compact sources, but is a signature of the whole population of structures that exist in the cloud, including more extended and elongated structures