arXiv subjects

B. Reipurth

Publications and source records attributed to B. Reipurth.

At least 19 recordsLinked to original sources

arXiv2025

Thackeray's globules in IC 2944: the rocket effect revisited by ALMA

The prominent Thackeray's globules are a collection of cloudlets seen in silhouette against the bright emission of the IC 2944 HII region, ionized by the Collinder 249 cluster of early-type stars (placed at 2331$\pm$30 pc, derived from a Gaia DR3 analysis of the parallaxes of 11 massive stars). Here we present the analysis of Band 3 ALMA data that reveals the cold emission (continuum and molecular) associated with the neutral gas and its kinematic behavior. Many of the globules follow a linear velocity gradient that can be explained as the result of an acceleration process due to the rocket effect, where freshly ionized material streams away from the globule, compressing and accelerating it. We identified 46 globules (12 of which are new detections), measured their kinematics, and estimated their densities and masses. At least 5 of them are associated with emission of dense molecular tracers and/or millimeter continuum sources and have indications of possible gravitational collapse. We applied a simple model for the acceleration of the globules which accounts for the observed kinematics. In this scenario only the most massive of the globules will be able to gravitationally collapse before being completely destroyed, in the process reaching speeds of tens km/s, and potentially becoming low-mass walkaway/runaway protostars.

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arXiv2024

iSHELL $K$-band Survey of Class I and Flat Spectrum Sources: Magnetic field measurements in the protostellar phase

We perform the first magnetic field strength survey of Class I and Flat Spectrum (FS) sources using $K$-band observations with iSHELL. We obtained new observations of 42 Class I and FS sources and additionally included 10 sources from the archive. We detect photospheric lines in 44 of the sources, in addition to Br$\gamma$, H$_2$, and CO emission in several objects. We model the photospheric absorption lines of 32 Class I and FS sources and measure their magnetic field strengths, $K$-band temperatures, gravities, projected rotational velocities, and infrared veiling values. We put the physical properties of Class I and FS sources in context by comparing them to the values derived for a sample of Class II sources. We find that a) the average magnetic field strength of Class I and FS sources $\langle B \rangle=2.0\pm0.15$ kG is consistent with the average magnetic field strength of Class II sources $\langle B \rangle=1.8\pm0.15$ kG, and b) the average gravity of Class I and FS objects $\log{g}=3.43\pm0.07$ is lower than the average gravity of Class II sources $\log{g}=3.75\pm0.04$, although there is significant overlap between both gravity distributions. Furthermore, using stellar evolutionary models, we deduce that Class I and FS sources have a median age of $\sim$0.6 Myr, and are, as a group, younger than the Class II stars with a median age of $\sim$3 Myr. Our results confirm that Class I and FS sources host strong magnetic fields on their photospheres. Thus, it is likely that these sources accrete disk material through a magnetosphere similar to the more evolved T Tauri stars.

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arXiv2024

New Herbig-Haro Objects associated with Embedded Sources

We continue to present the results of the Byurakan Narrow Band Imaging Survey (BNBIS). The main goal of this survey is to search for Herbig-Haro (HH) objects and jets in Galactic dark clouds. In this work we present the results of the search in the vicinity of infrared sources that are bright in the WISE survey and embedded in the dark clouds. The survey is performed with the 1 m Schmidt telescope of Byurakan Observatory, lately equipped with a new CCD detector, which allows to obtain one square degree images of the sky in various filters. Narrow-band filters were used to obtain Halpha and [S II] images, and a medium-width filter was used for the continuum imaging. New HH flows and knots were found near six embedded IR sources, which constitutes a significant proportion of the objects observed. At least two of the newly found HH flows (HH 1226 and HH 1227) lie in isolated dark clouds, thus pointing to active star formation in these regions. Other flows are also located in detached and dense globules or filaments. The length of the HH 1228 flow is about 1 pc; it has also a molecular hydrogen counterpart of the same extension. Coordinates, charts, detailed descriptions and distance estimates are provided. The lower limits of bolometric luminosities of the source stars are typical for low-mass young stellar objects.

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arXiv2021

The Effects of Starspots on Spectroscopic Mass Estimates of Low-mass Young Stars

Magnetic fields and mass accretion processes create dark and bright spots on the surface of young stars. These spots manifest as surface thermal inhomogeneities, which alter the global temperature measured on the stars. To understand the effects and implications of these starspots, we conducted a large iSHELL high-resolution infrared spectroscopic survey of T Tauri stars in Taurus-Auriga and Ophiuchus star-forming regions. From the K band spectra, we measured stellar temperatures and magnetic field strengths using a magnetic radiative transfer code. We compared our infrared-derived parameters against literature optical temperatures and found a) a systematic temperature difference between optical and infrared observations, and b) a positive correlation between the magnetic field strengths and the temperature differences. The discrepant temperature measurements imply significant differences in the inferred stellar masses from stellar evolutionary models. To discern which temperature better predicts the mass of the star, we compared our model-derived masses against dynamical masses measured from ALMA and PdBI for a sub-sample of our sources. From this comparison we conclude that, in the range of stellar masses from 0.3 to 1.3 $\rm M_\odot$, neither infrared nor optical temperatures perfectly reproduce the stellar dynamical masses. But, on average, infrared temperatures produce more precise and accurate stellar masses than optical ones.

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arXiv2021

FORCAST imaging of two small nearby Clusters: The Coronet and B59

We present mid infrared imaging of two young clusters, the Coronet in the CrA cloud core and B59 in the Pipe Nebula, using the FORCAST camera on the Stratospheric Observatory for Infrared Astronomy. We also analyze Herschel Space Observatory PACS and SPIRE images of the associated clouds. The two clusters are at similar, and very close, distances. Star formation is ongoing in the Coronet, which hosts at least one Class 0 source and several pre-stellar cores, which may collapse and form stars. The B59 cluster is older, although it still has a few Class I sources, and is less compact. The CrA cloud has a diameter of about 0.16 pc, and we determine a dust temperature of 15.7 K and a star formation efficiency of about 27 %, while the B59 core is approximately twice as large, has a dust temperature of about 11.4 K and a star formation efficiency of about 14 %. We infer that the gas densities are much higher in the Coronet, which has also formed intermediate mass stars, while B59 has only formed low-mass stars.

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arXiv2020

Near-infrared time-series photometry in the field of Cygnus OB2 association II. Mapping the variability of candidate members

We present the results of a J, H, and K photometric variability survey of the central 0.78 square degrees of the young OB association Cygnus OB2. We used data observed with the Wide-Field CAMera at the United Kingdom Infrared Telescope in 2007 (spanning 217 days) to investigate the light curves of 5083 low mass candidate members in the association and explore the occurrence and main characteristics of their near-infrared variability. We identified 2529 stars ($\sim$50$\%$ of the sample) with significant variability with time-scales ranging from days to months. We classified the variable stars into the following three groups according to their light curve morphology: periodic variability (1697 stars), occultation variability (124 stars), and other types of variability (726 stars). We verified that the disk-bearing stars in our sample are significantly more variable in the near-infrared than diskless stars, with a steep increase in the disk-fraction among stars with higher variability amplitude. We investigated the trajectories described by variable stars in the color-space and measured slopes for 335 stars describing linear trajectories. Based on the trajectories in the color-space, we inferred that the sample analyzed is composed of a mix of young stars presenting variability due to hot and cold spots, extinction by circumstellar material, and changes in the disk emission in the near-infrared. We contemplated using the use of near-infrared variability to identify disk-bearing stars and verified that 53.4$\%$ of the known disk-bearing stars in our sample could have been identified as such based solely on their variability. We present 18 newly identified disk-bearing stars and 14 eclipsing binary candidates among CygOB2 lower-mass members.

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arXiv2019

Halpha emission-line stars in molecular clouds III. Canis Major

A deep objective-prism survey for H-alpha emission stars towards the Canis Major star-forming clouds was performed. A total of 398 Halpha emitters were detected, 353 of which are new detections. There is a strong concentration of these H-alpha emitters towards the molecular clouds surrounding the CMa~OB1 association, and it is likely that these stars are young stellar objects recently born in the clouds. An additional population of H-alpha emitters is scattered all across the region, and probably includes unrelated foreground dMe stars and background Be stars. About 90% of the H-alpha emitters are detected by WISE, of which 75% was detected with usable photometry. When plotted in a WISE colour-colour diagram it appears that the majority are Class II YSOs. Coordinates and finding charts are provided for all the new stars, and coordinates for all the detections. We searched the Gaia-DR2 catalogue and from 334 Halpha emission stars with useful parallaxes, we selected a subset of 98 stars that have parallax errors of less than 20% and nominal distances in the interval 1050 to 1350 pc that surrounds a strong peak at 1185 pc in the distance distribution. Similarly, Gaia distances were obtained for 51 OB-stars located towards Canis Major and selected with the same parallax errors as the H-alpha stars. We find a median distance for the OB stars of 1182 pc, in excellent correspondence with the distance from the H-alpha stars. Two known runaway stars are confirmed as members of the association. Finally, two new Herbig-Haro objects are identified.

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arXiv2019

Silicate features in the circumstellar envelopes of the Class~I binary driving source of HH250

We investigate the silicate feature of the two Class I components of HH250-IRS, a resolved binary system with a separation of $0''53$ driving a Herbig-Haro flow. Each component has its own circumstellar envelope, and the system is surrounded by a circumbinary disk. We have carried out low resolution spectroscopy in the 8-13$μ$m range using VISIR at ESO's Very Large Telescope. The silicate features of both sources are clearly different. The NW component has a broad, smooth absorption profile lacking structure. The SE component shows the silicate feature in emission, with structure longwards of 9.5$μ$m indicating the presence of crystalline dust in the dominant form of forsterite. The apparent lack of an absorption feature caused by foreground dust is probably due to the filling of the band with emission by amorphous silicates in the envelope of the object. Despite their virtually certain coevality, the differences in the components of the HH250-IRS binary are most likely due to markedly different circumstellar environments. The NW component displays an unevolved envelope, whereas dust growth and crystallization has taken place in the SE component. The weak or absent signatures of enstatite in the latter are fairly unusual among envelopes with crystalline dust, and we tentatively relate it to a possible wide gap or an inner truncation of the disk already hinted in previous observations by a drop in the $L'$-band flux, which might indicate that the SE component could actually be a very close binary. We speculate that the clear differences between the silicate feature spectra of both components of HH250-IRS may be due either to disk evolution sped up by multiplicity, or by accretion variability leading to episodes of crystal formation.

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arXiv2017

Proper motions of the HH1 jet

We describe a new method for determining proper motions of extended objects, and a pipeline developed for the application of this method. We then apply this method to an analysis of four epochs of [S~II] HST images of the HH~1 jet (covering a period of $\sim 20$~yr). We determine the proper motions of the knots along the jet, and make a reconstruction of the past ejection velocity time-variability (assuming ballistic knot motions). This reconstruction shows an "acceleration" of the ejection velocities of the jet knots, with higher velocities at more recent times. This acceleration will result in an eventual merging of the knots in $\sim 450$~yr and at a distance of $\sim 80"$ from the outflow source, close to the present-day position of HH~1.

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arXiv2016

The time evolution of HH~2 from four epochs of HST images

We have analyzed four epochs of H$α$ and [S~II] HST images of the HH~1/2 outflow (covering a time interval from 1994 to 2014) to determine proper motions and emission line fluxes of the knots of HH~2. We find that our new proper motions agree surprisingly well with the motions measured by Herbig \& Jones (1981), although there is partial evidence for a slight deceleration of the motion of the HH~2 knots from 1945 to 2014. We also measure the time-variability of the H$α$ intensities and the [S~II]/H$α$ line ratios, and find that knots H and A have the largest intensity variabilities (in $1994\to 2014$). Knot H (which now dominates the HH~2 emission) has strengthened substantially, while keeping an approximately constant [S~II]/H$α$ ratio. Knot A has dramatically faded, and at the same time has had a substantial increase in its [S~II]/H$α$ ratio. Possible interpretations of these results are discussed.

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arXiv2016

The time evolution of HH 1 from four epochs of HST images

We present an analysis of four epochs of H$α$ and [S II] $λλ$ 6716/6731 HST images of HH 1. For determining proper motions we explore a new method based on analysis of spatially degraded images obtained convolving the images with wavelet functions of chosen widths. With this procedure we are able to generate maps of proper motion velocities along and across the outflow axis, as well as (angularly integrated) proper motion velocity distributions. From the four available epochs, we find the time evolution of the velocities, intensities and spatial distribution of the line emission. We find that over the last two decades HH 1 shows a clear acceleration. Also, the H$α$ and [S II] intensities have first dropped, and then recovered in the more recent (2014) images. Finally, we show a comparison between the two available HST epochs of [O III] $λ$ 5007 (1994 and 2014), in which we see a clear drop in the value of the [O III]/H$α$ ratio.

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arXiv2016

The intermediate-mass star-forming region Lynds 1340. An optical view

We have performed an optical spectroscopic and photometric search for young stellar objects associated with the molecular cloud Lynds 1340, and examined the structure of the cloud by constructing an extinction map, based on SDSS data. The new extinction map suggests a shallow, strongly fragmented cloud, having a mass of some 3700~Msun. Longslit spectroscopic observations of the brightest stars over the area of L1340 revealed that the most massive star associated with L1340 is a B4 type, about 5 solar mass star. The new spectroscopic and photometric data of the intermediate mass members led to a revised distance of 825 (+110 /-80) pc, and revealed seven members of the young stellar population with M > 2 solar masses. Our search for H alpha emission line stars, conducted with the Wide Field Grism Spectrograph 2 on the 2.2-meter telescope of the University of Hawaii and covering a 30 arcmin x 40 arcmin area, resulted in the detection of 75 candidate low-mass pre-main sequence stars, 58 of which are new. We constructed spectral energy distributions of our target stars, based on SDSS, 2MASS, Spitzer, and WISE photometric data, derived their spectral types, extinctions, and luminosities from BVRIJ fluxes, estimated masses by means of pre-main sequence evolutionary models, and examined the disk properties utilizing the 2-24 micron interval of the spectral energy distribution. We measured the equivalent width of the H alpha lines and derived accretion rates. The optically selected sample of pre-main sequence stars has a median effective temperature of 3970 K, stellar mass 0.7 Msun, and accretion rate of 7.6 10^{-9} Msun/yr.

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arXiv2014

Collisionally excited filaments in HST H$α$ and H$β$ images of HH~1/2

We present new H$α$ and H$β$ images of the HH~1/2 system, and we find that the H$α$/H$β$ ratio has high values in ridges along the leading edges of the HH~1 bow shock and of the brighter condensations of HH~2. These ridges have H$α$/H$β=4\to 6$, which is consistent with collisional excitation from the $n=1$ to the $n=3$ and 4 levels of hydrogen in a gas of temperatures $T=1.5\to 10\times 10^4$~K. This is therefore the first direct proof that the collisional excitation/ionization region of hydrogen right behind Herbig-Haro shock fronts is detected.

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arXiv2014

Radio Continuum Sources associated with the HH~92 and HH~34 Jets

We present high angular resolution, high sensitivity 8.46 GHz (3.6 cm) radio continuum observations made toward the core of the HH~92 outflow with the Very Large Array in 2002-2003 and with the Expanded Very Large Array in 2011. We detect a group of three compact sources distributed in a region 2$''$ in extension and discuss their nature. We conclude that one of the objects (VLA 1) is the exciting source of the giant outflow associated with HH~92. In the case of HH~34 we present new 43.3 GHz (7 mm) observations that reveal the presence of a structure associated with the exciting source and elongated perpendicular to the highly collimated optical jet in the region. We propose that this 7 mm source is a circumstellar disk with radius of $\sim$80 AU and mass of $\sim$0.21 $M_\odot$.

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arXiv2013

Stellar and circumstellar properties of visual binaries in the Orion Nebula Cluster

Our general understanding of multiple star and planet formation is primarily based on observations of young multiple systems in low density regions like Tau-Aur and Oph. Since many, if not most, of the stars are born in clusters, observational constraints from young binaries in those environments are fundamental for understanding both the formation of multiple systems and planets in multiple systems throughout the Galaxy. We build upon the largest survey for young binaries in the Orion Nebula Cluster (ONC) which is based on Hubble Space Telescope observations to derive both stellar and circumstellar properties of newborn binary systems in this cluster environment. We present Adaptive Optics spatially-resolved JHKL'-band photometry and K-band R$\sim$\,5000 spectra for a sample of 8 ONC binary systems from this database. We characterize the stellar properties of binary components and obtain a census of protoplanetary disks through K-L' color excess. For a combined sample of ONC binaries including 7 additional systems with NIR spectroscopy from the literature, we derive mass ratio and relative age distributions. We compare the stellar and circumstellar properties of binaries in ONC with those in Tau-Aur and Oph from samples of binaries with stellar properties derived for each component from spectra and/or visual photometry and with a disk census obtained through K-L color excess. The mass ratio distribution of ONC binaries is found to be indistinguishable from that of Tau-Aur and, to some extent, to that of Oph in the separation range 85-560\,AU and for primary mass in the range 0.15 to 0.8\,M$_{\sun}$.A trend toward a lower mass ratio with larger separation is suggested in ONC binaries which is not seen in Tau-Aur binaries.The components of ONC binaries are found to be significantly more coeval than the overall ONC population and as coeval as components of binaries in Tau-Aur and Oph[...]

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arXiv2008

High Angular Resolution Observations at 7-mm of the Core of the Quadrupolar HH 111/121 Outflow

We present sensitive, high angular resolution ($0\rlap.{''}05$) VLA continuum observations made at 7 mm of the core of the HH 111/121 quadrupolar outflow. We estimate that at this wavelength the continuum emission is dominated by dust, although a significant free-free contribution ($\sim$30%) is still present. The observed structure is formed by two overlapping, elongated sources approximately perpendicular to each other as viewed from Earth. We interpret this structure as either tracing two circumstellar disks that exist around each of the protostars of the close binary source at the core of this quadrupolar outflow or a disk and a jet perpendicular to it. Both interpretations have advantages and disadvantages, and future high angular resolution spectroscopic millimeter observations are required to favor one of them in a more conclusive way.

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arXiv2006

Anatomy of HH 111 from CO observations : a bow shock driven molecular outflow

We present millimeter line observations of the HH 111 outflow and its driving source. The molecular gas emission observed with IRAM 30m and the CSO reveals a small condensation of cold and dense gas. The low-velocity outflow has been mapped with the IRAM PdBI interferometer. The cold gas is distributed in a hollow cylinder surrounding the optical jet. The formation of this cavity and its kinematics are well accounted for in the frame of outflow gas entrainment by jet bow shocks. Evidence of gas acceleration is found along the cavity walls, correlated with the presence of optical bow shocks. The cavity has been expanding with a mean velocity of 4 km/s on a timescale of 8700 yr, similar to the dynamical age of the optical jet. The separation of the inner walls reaches 8"-10", which matches the transverse size of the wings in the bow shock. CSO observations of the J=7-6 line show evidence of a high-velocity and hot gas component (T=300-1000 K) with a low filling factor, associated with shocked molecular gas in the jet. [CI] observations are consistent with C-type non-dissociative shocks. Mapping of the high-velocity molecular bullets B1-B3 located beyond the optical jet, with the PdBI, reveals small structures of 3" by 7" flattened perpendicular to the flow direction. They are made of cold gas of moderate density(a few 10^3 cm-3). The bullets appear to expand into the low-density surrounding medium. We conclude that they are probably shocked gas knots resulting from past time-variable ejections in the jet.

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arXiv2005

Proper Motions of the HH 47 Jet Observed with the Hubble Space Telescope

We present a proper motion study of the shock waves within the classic stellar jet HH 47 based on Hubble Space Telescope H-alpha and [S II] images of the region taken over two epochs. Individual knots within the jet and in the bow shock/Mach disk working surface of HH 47A move significantly in the five years that separate the images, and the excellent spatial resolution of HST makes it possible to measure the proper motions with enough precision to easily observe differential motions throughout the flow. The bright portion of the jet emerges at 37.5 +/- 2.5 degrees from the plane of the sky with an average velocity of 300 km/s. Dynamical ages of the shock waves in the jet range from a few decades for knots recently ejected by the source to ~ 1300 years for the faint extended bow shock HH 47D. The jet curves, but motions of knots in the jet are directed radially away from the exciting source, and velocity variability in the flow drives the shock waves that heat the jet internally. The jet orientation angle varies with time by about 15 degrees, and currently points to the northwestern portion of a cavity outlined by a reflection nebula, where a quasi-stationary shock deflects the jet. The major working surface HH 47A is more complex than a simple bow shock/Mach disk, and contains numerous clumps that move relative to one another with velocities of ~ +/- 40 km/s. Small clumps or instabilities affect the Mach disk, and dense clumps may move all the way through the working surface to cause the bumpy morphology seen at the bow shock. A localized area between the bow shock and Mach disk varies significantly between the two sets of images.

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