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Star Formation in the Era of the Three Great Observatories
This paper summarizes contributions and suggestions as presented at theChandra Workshop Star Formation in the Era of Three Great Observatoriesconducted in July 2005. One of the declared goals of the workshop was toraise recognition within the star formation research community about thesensible future utilization of the space observatories Spitzer, Hubble,and Chandra in their remaining years of operation to tackle imminentquestions of our understanding of stellar formation and the earlyevolution of stars. A white paper was generated to support thecontinuous and simultaneous usage of observatory time for star formationresearch. The contents of this paper have been presented and discussedat several other meetings during the course of 2005 and January 2006.
| Faint emission lines in the Galactic HII regions M16, M20 and NGC 3603*
We present deep echelle spectrophotometry of the Galactic HII regionsM16, M20 and NGC 3603. The data have been taken with the Very LargeTelescope Ultraviolet-Visual Echelle Spectrograph in the 3100-10400Å range. We have detected more than 200 emission lines in eachregion. Physical conditions have been derived using different continuumand line intensity ratios. We have derived He+,C++ and O++ abundances from pure recombinationlines as well as collisionally excited lines (CELs) for a large numberof ions of different elements. We have obtained consistent estimationsof the temperature fluctuation parameter, t2, using differentmethods. We also report the detection of deuterium Balmer lines up toDδ (M16) and to Dγ (M20) in the blue wings of the hydrogenlines, which excitation mechanism seems to be continuum fluorescence.The temperature fluctuation paradigm agrees with the results obtainedfrom optical CELs, and the more uncertain ones from far-infraredfine-structure CELs in NGC 3603, although, more observations coveringthe same volume of the nebula are necessary to obtain solid conclusions.
| Dynamical H II Region Evolution in Turbulent Molecular Clouds
We present numerical radiation-hydrodynamic simulations of the evolutionof H II regions formed in an inhomogeneous medium resulting fromturbulence simulations. We find that the filamentary structure of theunderlying density distribution produces a highly irregular shape forthe ionized region, in which the ionization front escapes to largedistances in some directions within 80,000 years. In other directions,on the other hand, neutral gas in the form of dense globules persistswithin 1 pc of the central star for the full duration of our simulation(400,000 years). Divergent photoablation flows from these globulesmaintain an rms velocity in the ionized gas that is close to the ionizedsound speed. Simulated images in optical emission lines showmorphologies that are in strikingly detailed agreement with thoseobserved in real H II regions.
| Balmer and Paschen Jump Temperature Determinations in Low-Metallicity Emission-Line Galaxies
We have used the Balmer and Paschen jumps to determine the temperaturesof the H+ zones of a total sample of 47 H II regions. TheBalmer jump was used on MMT spectrophotometric data of 22low-metallicity H II regions in 18 blue compact dwarf (BCD) galaxies andof one H II region in the spiral galaxy M101. The Paschen jump was usedon spectra of 24 H II emission-line galaxies selected from the DataRelease 3 of the Sloan Digital Sky Survey (SDSS). To derive thetemperatures, we have used a Monte Carlo technique varying the electrontemperature in the H+ zone, the extinction of the ionized gasand that of the stellar population, the relative contribution of theionized gas to the total emission, and the star formation history to fitthe spectral energy distribution of the galaxies. For the MMT spectra,the fit was done in the wavelength range 3200-5200 Å, whichincludes the Balmer discontinuity, and for the SDSS spectra, in thewavelength range 3900-9200 Å, which includes the Paschendiscontinuity. We find for our sample of H II regions that thetemperatures of the O2+ zones determined from thenebular-to-auroral line intensity ratio of doubly ionized oxygen [O III]λλ(4959+5007)/λ4363 do not differ, in a statisticalsense, from the temperatures of the H+ zones determined fromfitting the Balmer and Paschen jumps and the spectral energydistributions (SEDs). We cannot rule out small temperature differencesof the order of 3%-5%.
| Spectacular Spitzer Images of the Trifid Nebula: Protostars in a Young, Massive-Star-forming Region
Spitzer IRAC and MIPS images of the Trifid Nebula (M20) reveal itsspectacular appearance in infrared light, highlighting the nebula'sspecial evolutionary stage. The images feature recently formed massiveprotostars and numerous young stellar objects, and a single O star thatilluminates the surrounding molecular cloud from which it formed, andunveil large-scale, filamentary dark clouds. Multiple protostars aredetected in the infrared, within the cold dust cores of TC3 and TC4,which were previously defined as Class 0. The cold dust continuum coresof TC1 and TC2 contain only one protostar each. The Spitzer color-colordiagram allowed us to identify ~160 young stellar objects (YSOs) andclassify them into different evolutionary stages. The diagram alsorevealed a unique group of YSOs that are bright at 24 μm but have thespectral energy distribution peaking at 5-8 μm. Despite expectationthat Class 0 sources would be ``starless'' cores, the Spitzer images,with unprecedented sensitivity, uncover mid-infrared emission from theseClass 0 protostars. The mid-infrared detections of Class 0 protostarsshow that the emission escapes the dense, cold envelope of youngprotostars. The mid-infrared emission of the protostars can be fit bytwo temperatures of 150 and 400 K; the hot core region is probablyoptically thin in the mid-infrared regime, and the size of hot core ismuch smaller than that of the cold envelope. The presence of multipleprotostars within the cold cores of Class 0 objects implies thatclustering occurs at this early stage of star formation. The mostmassive star in the TC3 cluster is located at the center of the clusterand at the bottom of the gravitational potential well.
| X-Ray and Infrared Point Source Identification and Characteristics in the Embedded, Massive Star-Forming Region RCW 38
We report on results of a 96.7 ks Chandra observation of one of theyoungest, most embedded, and most massive young stellar clusters studiedin X-rays: RCW 38. We detect 460 sources in the field, of which 360 areconfirmed to be associated with the RCW 38 cluster. The cluster membersrange in luminosity from 1030 to 1033.5 ergss-1. Over 10% of the cluster members with over 100 countsexhibit flares, while about 15% of the cluster members with over 30counts are variable. Of the sources identified as cluster members, 160have near-infrared (NIR) counterparts either in the Two Micron All SkySurvey database or detected via Very Large Telescope observations. Ofthese, about 20% appear to have optically thick disks. An additional 353members are identified through NIR observations, of which at least 50%possess optically thick disks. We fit over 100 X-ray sources as absorbedRaymond-Smith-type plasmas and find that the column to the clustermembers varies from 1021.5 to 1023cm-2. We compare the gas to dust absorption signatures inthese stars and findNH=AV(2×1021) cm-2. Wefind that the cluster contains 31 candidate OB stars and is centeredabout 10" (0.1 pc) west of the primary source of the ionization, the O5star IRS 2. The cluster has a peak central density of about 400 X-raysources pc-2. We estimate that the total cluster membershipexceeds 2000 stars.
| Cloud Fragmentation and Proplyd-like Features in H II Regions Imaged by the Hubble Space Telescope
We have analyzed Hubble Space Telescope ACS and WFPC2 new and archivalimages of eight H II regions to look for new protoplanetary disks(proplyds) similar to those found in the Orion Nebula. We find a wealthof features similar in size (although many are larger) to the brightcusps around the Orion Nebula proplyds. None of them, however, containsa definitive central star. From this, we deduce that the new cusps maynot be proplyds but instead fragments of molecular cloud material. Outof all the features found in the eight H II regions examined, only one,an apparent edge-on silhouette in M17, may have a central star. Thisfeature might join the small number of bona fide proplyds found outsidethe Orion Nebula, in M8, M20, and possibly M16. In line with the resultsfound recently by Smith et al., the paucity of proplyds outside theOrion Nebula can be explained by their transient nature, as well as bythe specific environmental conditions under which they can be observed.Several fragments are seen as dark silhouettes against a brightbackground. We have reanalyzed those found in IC 2944 by Reipurth et al.and found new, similar ones in M16. None of these fragments contains acentral star, and we exclude the possibility that they are disks.Reipurth et al. concluded that the IC 2944 silhouettes are not starforming. We argue here that their assumption of a constant optical depthfor these fragments is not physical and that it is more likely thatthese fragments are star forming, a condition that is supported,although not proved, by their shapes and distributions. The process ofcloud fragmentation and photoevaporation produces a large number ofsmall fragments, while the size hierarchy expected in a photoevaporativeenvironment would not favor small fragments. The size distributionsobserved will constrain any future theories of cloud fragmentation. Onebright microjet candidate is found in M17, protruding from a large,limb-brightened fragment. A second, larger, jetlike feature, similar inshape and size to a Herbig-Haro jet, is found in Pismis 24. No centralstar appears to be associated with either of these jet candidates.Based on observations made with the NASA/ESA Hubble Space Telescopeobtained at the Space Telescope Science Institute, which is operated bythe Association of Universities for Research in Astronomy (AURA), Inc.,under NASA contract NAS5-26555.
| An empirical calibration of sulphur abundance in ionised gaseous nebulae
We have derived an empirical calibration of the abundance of S/H as afunction of the S{23} parameter, defined using the bright sulphur linesof [SII] and [SIII]. Contrary to the case for the widely used O{23}parameter, the calibration remains single valued up to the abundancevalues observed in the disk HII regions. The calibration is based on alarge sample of nebulae for which direct determinations of electrontemperatures exist and the sulphur chemical abundances can be directlyderived. ICFs, as derived from the [SIV] 10.52 μ emission line (ISOobservations), are shown to be well reproduced by Barker's formula for avalue of α = 2.5. Only about 30% of the objects in the samplerequire ICFs larger than 1.2. The use of the proposed calibration opensthe possibility of performing abundance analysis with red to IRspectroscopic data using S/H as a metallicity tracer.
| Deepsky delights.
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| Deep echelle spectrophotometry of S 311, a Galactic HII region located outside the solar circle
We present echelle spectrophotometry of the Galactic HII region S 311.The data have been taken with the Very Large TelescopeUltraviolet-Visual Echelle Spectrograph in the 3100-10400 Årange.We have measured the intensities of 263 emission lines; 178 arepermitted lines of H0, D0 (deuterium),He0, C0, C+, N0,N+, O0, O+, S+,Si0, Si+, Ar0 and Fe0; someof them are produced by recombination and others mainly by fluorescence.Physical conditions have been derived using different continuum- andline-intensity ratios. We have derived He+, C++and O++ ionic abundances from pure recombination lines aswell as abundances from collisionally excited lines for a large numberof ions of different elements. We have obtained consistent estimationsof t2 applying different methods. We have found that thetemperature fluctuations paradigm is consistent with theTe(HeI) versus Te(HI) relation for HII regions, incontrast with what has been found for planetary nebulae. We report thedetection of deuterium Balmer lines up to Dδ in the blue wings ofthe hydrogen lines, whose excitation mechanism seems to be continuumfluorescence.
| A Parsec-Scale Outflow in the Rosette Molecular Cloud?
We report on new observations of a purported parsec-scale outflow in thehostile environment at the boundary of the Rosette Nebula, a well-knownH II region driven by several O stars in the open cluster NGC 2244, andthe Rosette Molecular Cloud (RMC). Several emission features were firstreported by Ybarra & Phelps in 2004 , but with only optical [S II]imaging, their nature could not then be established. Our newnear-infrared (NIR) H2 imaging observations reveal bulletedNIR emission between a Two Micron All Sky Survey (2MASS) NIR excesspoint source and the optical [S II] emission for RMC C of Ybarra &Phelps. Analysis of the 2MASS colors indicates that the point source islikely to be a Class I young stellar object (YSO). Together theseresults imply that RMC C is in fact part of a true YSO outflow, nowdesignated HH 871. The presence of additional [S II] emission,apparently connected to the HH 871 outflow but separated by ~1.2 pc,assuming a distance of 1600 pc for the RMC, also lends support to theYbarra & Phelps hypothesis that a parsec-scale outflow is present inthis harsh ionizing environment.
| Proper Motion of the Irradiated Jet HH 399 in the Trifid Nebula
HH 399 is one of the first Herbig-Haro flows recognized to be irradiatedby the UV radiation of the massive O7.5 star in the Trifid Nebula. Wepresent the proper motion of the first irradiated jet, based on twoepochs of Hubble Space Telescope (HST) observations of HH 399 separatedby nearly 5 yr, using Hα and [S II] line filters. High propermotion with continuous velocities between 200+/-55 and 528+/-24 kms-1 is detected in both lines along the 18" extent of the jetaxis. The irradiated fully ionized jet consists of numerous knots alongthe jet but also shows evidence for a number of isolated blob likestructures running immediately outside the jet with lower transversevelocities. The transverse velocities combined with radial velocitymeasurements indicate that the jet axis lies away from the plane of thesky by only a few degrees. We argue that the jet is fully ionized, basedon a [S II]/Hα line ratio, as well as radio continuum emissiondetected from the full extent of the jet at a 3.6 cm wavelength. Thestellar mass-loss rate producing HH 399 is estimated to be~2×10-6 Msolar yr-1.
| Discovery of Extremely Embedded X-Ray Sources in the R Coronae Australis Star-forming Core
With the XMM-Newton and Chandra observatories, we detected two extremelyembedded X-ray sources in the R Corona Australis (R CrA) star-formingcore, near IRS 7. These sources, designated as XE andXW, have X-ray absorption columns of ~3×1023cm-2 equivalent to AV~180 mag. They are associatedwith the VLA centimeter radio sources 10E and 10W, respectively;XW is the counterpart of the near-infrared source IRS 7,whereas XE has no K-band counterpart above 19.4 mag. Thisindicates that XE is younger than typical Class I protostars,probably a Class 0 protostar, or in an intermediate phase between Class0 and Class I. The X-ray luminosity of XE varied between29
| Carbon, Nitrogen, and Oxygen Galactic Gradients: A Solution to the Carbon Enrichment Problem
Eleven models of Galactic chemical evolution, differing in the carbon,nitrogen, and oxygen yields adopted, have been computed to reproduce theGalactic O/H values obtained from H II regions. All the models fit theoxygen gradient, but only two models also fit the carbon gradient, thosebased on carbon yields that increase with metallicity owing to stellarwinds in massive stars (MSs) and decrease with metallicity owing tostellar winds in low- and intermediate-mass stars (LIMSs). Thesuccessful models also fit the C/O versus O/H evolution history of thesolar vicinity obtained from stellar observations. We also compare thepresent-day N/H gradient and the N/O versus O/H and the C/Fe, N/Fe, O/Feversus Fe/H evolution histories of the solar vicinity predicted by ourtwo best models with those derived from H II regions and from stellarobservations. While our two best models fit the C/H and O/H gradients,as well as the C/O versus O/H history, only model 1 fits well the N/Hgradient and the N/O values for metal-poor stars but fails to fit theN/H values for metal-rich stars. Therefore, we conclude that our twobest models solve the C enrichment problem but that further work needsto be done on the N enrichment problem. By adding the C and O productionsince the Sun was formed predicted by models 1 and 2 to the observedsolar values, we find an excellent agreement with the O/H and C/H valuesof the solar vicinity derived from H II region O and C recombinationlines. Our results are based on an initial mass function (IMF) steeperthan Salpeter's a Salpeter-like IMF predicts C/H, N/H, and O/H ratioshigher than observed. One of the most important results of this paper isthat the fraction of carbon due to MSs and LIMSs in the interstellarmedium is strongly dependent on time and on the galactocentric distance;at present about half of the carbon in the interstellar medium of thesolar vicinity has been produced by MSs and half by LIMSs.
| Carbon and Oxygen Galactic Gradients: Observational Values from H II Region Recombination Lines
We present results of deep echelle spectrophotometry of eight Galactic HII regions located at Galactocentric distances between 6.3 and 10.4 kpc.The data have been taken with the Very Large Telescope UltravioletEchelle Spectrograph in the 3100-10360 Å range. We have derivedC++ and O++ abundances from recombination linesfor all the objects as well as O+ abundances from this kindof line for three of the nebulae. The intensity of recombination linesis almost independent of the assumed electron temperature as well as ofthe possible presence of spatial temperature variations or fluctuationsinside the nebulae. These data allow the determination of the gas-phaseC and O abundance gradients of the Galactic disk, of paramountimportance for chemical evolution models. This is the first time the Cgradient is derived from such a large number of H II regions distributedin such a wide range of Galactocentric distances. Abundance gradientsare found of the form Δlog(O/H)=-0.044+/-0.010 dexkpc-1, Δlog(C/H)=-0.103+/-0.018 dex kpc-1,and Δlog(C/O)=-0.058+/-0.018 dex kpc-1.Based on observations collected at the European Southern Observatory,Chile; proposals ESO 68.C-0149(A) and ESO 70.C-0008(A).
| Hubble Space Telescope and United Kingdom Infrared Telescope Observations of the Center of the Trifid Nebula: Evidence for the Photoevaporation of a Proplyd and a Protostellar Condensation
The Trifid Nebula (M20) is a well-known prominent optical H II regiontrisected by bands of obscuring dust lanes and excited by an O7.5 star,HD 164492A. Previous near-IR, mid-IR, and radio continuum observationsof the cluster of stars at the center of the Trifid Nebula indicated thepresence of circumstellar disks associated with hot stars with envelopesthat are photoionized externally by the UV radiation from the hotcentral star, HD 164492A. Using the WFPC2 on the Hubble Space Telescope,we present evidence of a resolved proplyd in Hα and [S II] lineemission from a stellar source emitting cool dust emission. Using theUnited Kingdom Infrared Telescope, an infrared observation of thestellar source with a proplyd indicates a late F to mid-G spectral type.We also note a remarkable complex of filamentary and sheetlikestructures that appear to arise from the edge of a protostellarcondensation. These observations are consistent with a picture in whichthe bright massive star HD 164492A is responsible for thephotoevaporation of protoplanetary disks of other less massive membersof the cluster, as well as the closest protostellar condensation facingthe central cluster. Using the evidence for a proplyd, we argue that themassive and intermediate-mass members of the cluster, HD 164492C (B6star) and HD 164492 (Herbig Be star), have disks associated with them.
| Astrophysical parameters of Galactic open clusters
We present a catalogue of astrophysical data for 520 Galactic openclusters. These are the clusters for which at least three most probablemembers (18 on average) could be identified in the ASCC-2.5, a catalogueof stars based on the Tycho-2 observations from the Hipparcos mission.We applied homogeneous methods and algorithms to determine angular sizesof cluster cores and coronae, heliocentric distances, mean propermotions, mean radial velocities, and ages. For the first time we derivedistances for 200 clusters, radial velocities for 94 clusters, and agesof 196 clusters. This homogeneous new parameter set is compared withearlier determinations, where we find, in particular, that the angularsizes were systematically underestimated in the literature.
| On the relationship between auroral and nebular oxygen line intensities in spectra of H II regions
We investigate relationships between observed auroral and nebular oxygenline fluxes in spectra of H ii regions. We find a relation that ismetallicity-dependent at low metallicities, but becomes independent ofmetallicity (within the uncertainties of the available data) above12+logO/H ~ 8.25, i.e. there is one-to-one correspondence (theff-relation) between auroral and nebular oxygen line fluxes in spectraof high-metallicity H ii regions. The ff-relation allows one to estimatethe flux in the auroral line from strong oxygen line measurements only.This solves the problem of the electron temperature (and, consequently,abundance) determination in high-metallicity H ii regions. Theff-relation confirms the basic idea of the “empirical”method, proposed by Pagel et al. (1979, MNRAS, 189, 95) a quarter of acentury ago, that the oxygen abundance in H ii region can be esimatedfrom the strong oxygen lines measurements only.
| The Impact of Space Experiments on our Knowledge of the Physics of the Universe
With the advent of space experiments it was demonstrated that cosmicsources emit energy practically across all the electromagnetic spectrumvia different physical processes. Several physical quantities givewitness to these processes which usually are not stationary; thosephysical observable quantities are then generally variable. Thereforesimultaneous multifrequency observations are strictly necessary in orderto understand the actual behaviour of cosmic sources. Space experimentshave opened practically all the electromagnetic windows on the Universe.A discussion of the most important results coming from multifrequencyphotonic astrophysics experiments will provide new inputs for theadvance of the knowledge of the physics, very often in its more extremeconditions. A multitude of high quality data across practically thewhole electromagnetic spectrum came at the scientific community'sdisposal a few years after the beginning of the Space Era. With thesedata we are attempting to explain the physics governing the Universeand, moreover, its origin, which has been and still is a matter of thegreatest curiosity for humanity. In this paper we will try to describethe last steps of the investigation born with the advent of spaceexperiments, to note upon the most important results and open problemsstill existing, and to comment upon the perspectives we can reasonablyexpect. Once the idea of this paper was well accepted by ourselves, wehad the problem of how to plan the exposition. Indeed, the exposition ofthe results can be made in different ways, following several points ofview, according to: - a division in diffuse and discrete sources; -different classes of cosmic sources; - different spectral ranges, whichimplies in turn a sub-classification in accordance with differenttechniques of observations; - different physical emission mechanisms ofelectromagnetic radiation; - different vehicles used for launching theexperiments (aircraft, balloons, rockets, satellites, observatories). Inorder to exhaustively present The Impact of Space Experiments on ourKnowledge of the Physics of the Universe it would then have beennecessary to write a kind of Encyclopaedia of the Astronomical SpaceResearch, which is not our desire. On the contrary, since our goal is toprovide an useful tool for the reader who has not specialized in spaceastrophysics and for the students, we decided to write this paper in theform of a review, the length of which can be still consideredreasonable, taking into account the complexity of the argumentsdiscussed. Because of the impossibility of realizing a complete pictureof the physics governing the Universe, we were obliged to select how toproceed, the subjects to be discussed the more or the less, or those tobe rejected. Because this work was born in the Ph.D. thesis of one of us(LSG) (Sabau-Graziati, 1990) we decided to follow the `astronomicaltradition' used there, namely: the spectral energy ranges. Although suchenergy ranges do not determine physical objects (even if in many casessuch ranges are used to define the sources as: radio, infrared, optical,ultraviolet, X-ray, γ-ray emitters), they do determine themethods of study, and from the technical point of view they define thetechnology employed in the relative experiments. However, since then wehave decided to avoid a deep description of the experiments, satellites,and observatories, simply to grant a preference to the physical results,rather than to technologies, however fundamental for obtaining thoseresults. The exposition, after an introduction (Section 1) and somecrucial results from space astronomy (Section 2), has been focussed intothree parts: the physics of the diffuse cosmic sources deduced fromspace experiments (Section 3), the physics of cosmic rays from ground-and space-based experiments (Section 4), and the physics of discretecosmic sources deduced from space experiments (Section 5). In this firstpart of the paper we have used the logic of describing the main resultsobtained in different energy ranges, which in turn characterize theexperiments on board space vehicles. Within each energy range we havediscussed the contributions to the knowledge of various kind of cosmicsources coming from different experiments. And this part is mainlyderived by the bulk of the introductory part of LSG's Ph.D. thesis. Inthe second part of the paper, starting from Section 6, we have preferredto discuss several classes of cosmic sources independently of the energyranges, mainly focussing the results from a multifrequency point ofview, making a preference for the knowledge of the physics governing thewhole class. This was decided also because of the multitude of new spaceexperiments launched in the last fifteen years, which would haverendered almost impossible a discussion of the results divided intoenergy ranges without weakening the construction of the entire puzzle.We do not pretend to cover every aspect of every subject consideredunder the heading of the physics of the universe. Instead a crosssection of essays on historical, modern, and philosophical topics areoffered and combined with personal views into tricks of the spaceastrophysics trade. The reader is, then, invited to accept this papereven though it obviously lacks completeness and the arguments discussedare certainly biased by a selection effect owed essentially to ourknowledge, and to it being of a reasonable length. Some parts of itcould seem, in certain sense, to belong to an older paper, in which the`news' is not reported. But this is owed to our own choice, just in fullaccord with the goals of the text: we want to present those resultswhich have, in our opinion, been really important, in the development ofthe science. These impacting results do not necessarily constitute thelast news. This text was formally closed just on the day of the launchof the INTEGRAL satellite: October 17, 2002. After that date onlyfinishing touches have been added.
| ISO Spectroscopy of Gas and Dust: From Molecular Clouds to Protoplanetary Disks
Observations of interstellar gas-phase and solid-state species in the2.4 200 m range obtained with the spectrometers on board the InfraredSpace Observatory (ISO) are reviewed. Lines and bands caused by ices,polycyclic aromatic hydrocarbons, silicates, and gas-phase atoms andmolecules (in particular H2, CO, H2O, OH, andCO2) are summarized and their diagnostic capabilitiesillustrated. The results are discussed in the context of the physicaland chemical evolution of star-forming regions, includingphoton-dominated regions, shocks, protostellar envelopes, and disksaround young stars.
| A Uniform Database of 2.2-16.5 μm Spectra from the ISOCAM CVF Spectrometer
We present all ISOCAM circular variable filter (CVF) spectra that covermore than one-third of the 2.2-16.5 μm spectral range of theinstrument. The 364 spectra have been classified according to theclassification system of Kraemer et al., as modified by Hodge et al. toaccount for the shorter wavelength range. Prior to classification, thespectra were processed and recalibrated to create a uniform database.Aperture photometry was performed at each wavelength centered on thebrightest position in each image field and the various spectral segmentsmerged into a single spectrum. The aperture was the same for all scalesizes of the images. Since this procedure differs fundamentally fromthat used in the initial ISOCAM calibration, a recalibration of thespectral response of the instrument was required for the aperturephotometry. The recalibrated spectra and the software used to createthem are available to the community on-line via the ISO Data Archive.Several new groups were added to the KSPW system to describe spectrawith no counterparts in either the SWS or PHT-S databases: CA, E/SA,UE/SA, and SSA. The zodiacal dust cloud provides the most commonbackground continuum to the spectral features, visible in almost 40% ofthe processed sources. The most characteristic and ubiquitous spectralfeatures observed in the CVF spectral atlas are those of theunidentified infrared bands (UIR), which are typically attributed toultraviolet-excited fluorescence of large molecules containing aromatichydrocarbons. The UIR features commonly occur superimposed on thezodiacal background (18%) but can also appear in conjunction with otherspectral features, such as fine-structure emission lines or silicateabsorption. In at least 13 of the galaxies observed, the pattern of UIRemission features has been noticeably shifted to longer wavelengths.Based on observations with the Infrared Space Observatory, a EuropeanSpace Agency (ESA) project with instruments funded by ESA Member States(especially the Principal Investigator countries: France, Germany, theNetherlands, and the United Kingdom) and with the participation of theInstitute of Space and Astronautical Science (ISAS) and the NationalAeronautics and Space Administration (NASA).
| A Very Large Array Search for Water Masers in Six H II Regions: Tracers of Triggered Low-Mass Star Formation
We present a search for water maser emission at 22 GHz associated withyoung low-mass protostars in six H II regions-M16, M20, NGC 2264, NGC6357, S125, and S140. The survey was conducted with the NRAO Very LargeArray from 2000 to 2002. For several of these H II regions, ours are thefirst high-resolution observations of water masers. We detected 16 watermasers: eight in M16, four in M20, three in S140, and one in NGC 2264.All but one of these were previously undetected. No maser emission wasdetected from NGC 6357 or S125. There are two principle results to ourstudy. (1) The distribution of water masers in M16 and M20 does notappear to be random but instead is concentrated in a layer of compressedgas within a few tenths of a parsec of the ionization front. (2)Significantly fewer masers are seen in the observed fields than expectedbased on other indications of ongoing star formation, indicating thatthe maser-exciting lifetime of protostars is much shorter in H IIregions than in regions of isolated star formation. Both of theseresults confirm predictions of a scenario in which star formation isfirst triggered by shocks driven in advance of ionization fronts andthen truncated ~105 yr later when the region is overrun bythe ionization front.
| Chandra Observation of the Trifid Nebula: X-Ray Emission from the O Star Complex and Actively Forming Pre-Main-Sequence Stars
The Trifid Nebula, a young star-forming H II region, was observed for 16hr by the ACIS-I detector on board the Chandra X-Ray Observatory. Wedetected 304 X-ray sources, 30% of which are hard sources and 70% ofwhich have near-infrared counterparts. Chandra resolved the HD 164492multiple system into a number of discrete X-ray sources. X-ray emissionis detected from components HD 164492A (an O7.5 III star that ionizesthe nebula), B and C (a B6 V star), and possibly D (a Be star).Component C is blended with an unidentified source to the northwest. HD164492A has a soft spectrum (kT~0.5 keV), while the component C blendshows much harder emission (kT~6 keV). This blend and other hard sourcesare responsible for the hard emission and Fe K line seen by ASCA, whichwas previously attributed entirely to HD 164492A. The soft spectrum ofthe O star is similar to emission seen from other single O stars and isprobably produced by shocks within its massive stellar wind. Lack ofhard emission suggests that neither a magnetically confined wind shocknor colliding wind emission is important in HD 164492A. A dozen starsare found to have flares in the field, and most of them arepre-main-sequence stars (PMS). Six sources with flares have both opticaland Two Micron All Sky Survey counterparts. These counterparts are notembedded, and thus it is likely that these sources are in a later stageof PMS evolution, possibly Class II or III. Two flare sources did nothave any near-IR, optical, or radio counterparts. We suggest that theseX-ray flare stars are in an early PMS stage (Class I or earlier). Wealso detected X-ray sources apparently associated with two massivestar-forming cores, TC 1 and TC 4. The spectra of these sources showhigh extinction and X-ray luminosities of (2-5)×1031ergs s-1. If these sources are Class 0 objects, it is unclearwhether their X-ray emission is due to solar-type magnetic activities,as in Class I objects, or to some other mechanism.
| The supernova remnant G 6.4-0.1 and its environment
Flux calibrated CCD images, in the Hα+[N II], S II, and [O III]emission lines, of a wide field around the supernova remnant G 6.4-0.1are presented. The low ionization images identify a front of enhanced SII/Hα+[N II] ratio along the east-west direction. This front isvery well correlated with the filamentary radio emission of the remnantas well as with molecular CO emission and may indicate the interactionof the primary blast wave with molecular clouds present in the vicinityof the remnant. We estimate a total Hα flux, corrected forinterstellar extinction, of 2 × 10-8 erg s-1cm-2, and a total S II flux of 1.1 × 10-8erg s-1 cm-2. The Hα+[N II] and S II imagesprovide evidence for the presence of emission from shock heated gas tothe south-west and to the east of the bulk of the known opticalemission, implying that the primary shock wave is able to driveradiative shocks into the interstellar clouds. The image in the mediumionization line of [O III] 5007 Å does not reveal any filamentarystructures. On the contrary, the emission is diffuse and very weak,close to our detection limit of 5 × 10-17 ergs-1 cm-2 arcsec-2 (3 σ), andappears to be mainly present in the south-east to north-west areas ofthe remnant. The long-slit spectra indicate significant extinction inall positions observed, while the measured variations are within the 3σ error. The [O III] emission in the spectra, whenever present, isweaker than the ^hbeta flux suggesting shock velocities around 70 kms-1 or less all around the remnant in accordance with the [OIII] imagery. Thus, the low shock velocities are a common characteristicof G 6.4-0.1 and not just of the areas where the spectra were acquired.The average sulfur line ratio suggests postshock electron densitiesbelow 120 cm-3 at the 3 σ limit.
| Searching for signs of triggered star formation toward IC 1848
We have carried out an in-depth study of three bright-rimmed cloudsSFO 11, SFO 11NE and SFO 11Eassociated with the HII region IC 1848, using observations carried outat the James Clerk Maxwell Telescope (JCMT) and the Nordic OpticalTelescope (NOT), plus archival data from IRAS, 2MASS and the NVSS. Weshow that the overall morphology of the clouds is reasonably consistentwith that of radiative-driven implosion (RDI) models developed topredict the evolution of cometary globules. There is evidence for aphotoevaporated flow from the surface of each cloud and, based upon themorphology and pressure balance of the clouds, it is possible thatD-critical ionisation fronts are propagating into the molecular gas. Theprimary O star responsible for ionising the surfaces of the clouds isthe 06V star HD 17505. Each cloud is associated witheither recent or ongoing star formation: we have detected 8 sub-mm coreswhich possess the hallmarks of protostellar cores and identify YSOcandidates from 2MASS data. We infer the past and future evolution ofthe clouds and demonstrate via a simple pressure-based argument that theUV illumination may have induced the collapse of the dense molecularcores found at the head of SFO 11 and SFO11E.
| Supernova remnants and γ-ray sources
Electronic Article Available from Elsevier Science.
| My researches at the infrared doors
As a historical and biographical introduction to this Conference, I givehere a brief review about my studies in infrared astronomy. I begunmaking regular observations in this unexplored (at that time) fieldmoving from the wavelengths just beyond the visible, where I discovered,for example, the galaxies then named Maffei 1 and Maffei 2, located inthe Zone of Avoidance. The analysis of the material thus collected,mainly aimed at studies on long period variables (LPVs), produced aseries of new and hardly predicted results. Further importantdevelopments of my researches in infrared are now expected from theongoing development of an Antarctica telescope for the mid-infraredbands. These bands were an almost unexplored range of the spectrum onlya few years ago: now the researches discussed in this meeting show howmany new fields of study have become active in them.
| Proper Motions of Open Star Clusters and the Rotation Rate of the Galaxy
The mean proper motions of 167 Galactic open clusters withradial-velocity measurements are computed from the data of the Tycho-2catalog using kinematic and photometric cluster membership criteria. Theresulting catalog is compared to the results of other studies. The newproper motions are used to infer the Galactic rotation rate at the solarcircle, which is found to be ω0=+24.6±0.8 km s-1 kpc-1.Analysis of the dependence of the dispersion of ω0 estimates onheliocentric velocity showed that even the proper motions of clusterswith distances r>3 kpc contain enough useful information to be usedin kinematic studies demonstrating that the determination of propermotions is quite justified even for very distant clusters.
| Embedded Clusters in Molecular Clouds
Stellar clusters are born embedded within giant molecular clouds (GMCs)and during their formation and early evolution are often only visible atinfrared wavelengths, being heavily obscured by dust. Over the past 15years advances in infrared detection capabilities have enabled the firstsystematic studies of embedded clusters in galactic molecular clouds. Inthis article we review the current state of empirical knowledgeconcerning these extremely young protocluster systems. From a survey ofthe literature we compile the first extensive catalog of galacticembedded clusters. We use the catalog to construct the mass function andestimate the birthrate for embedded clusters within 2 kpc of the sun. Wefind that the embedded cluster birthrate exceeds that of visible openclusters by an order of magnitude or more indicating a high infantmortality rate for protocluster systems. Less than 4-7% of embeddedclusters survive emergence from molecular clouds to become boundclusters of Pleiades age. The vast majority (90%) of stars that form inembedded clusters form in rich clusters of 100 or more members withmasses in excess of 50 Mȯ. Moreover, observations ofnearby cloud complexes indicate that embedded clusters account for asignificant (70-90%) fraction of all stars formed in GMCs. We review therole of embedded clusters in investigating the nature of the initialmass function (IMF) that, in one nearby example, has been measured overthe entire range of stellar and substellar mass, from OB stars tosubstellar objects near the deuterium burning limit. We also review therole embedded clusters play in the investigation of circumstellar diskevolution and the important constraints they provide for understandingthe origin of planetary systems. Finally, we discuss current ideasconcerning the origin and dynamical evolution of embedded clusters andthe implications for the formation of bound open clusters.
| The Wisconsin Hα Mapper Northern Sky Survey
The Wisconsin Hα Mapper (WHAM) has surveyed the distribution andkinematics of ionized gas in the Galaxy above declination -30°. TheWHAM Northern Sky Survey (WHAM-NSS) has an angular resolution of 1°and provides the first absolutely calibrated, kinematically resolved mapof the Hα emission from the warm ionized medium (WIM) within~+/-100 km s-1 of the local standard of rest. LeveragingWHAM's 12 km s-1 spectral resolution, we have modeled andremoved atmospheric emission and zodiacal absorption features from eachof the 37,565 spectra. The resulting Hα profiles reveal ionizedgas detected in nearly every direction on the sky with a sensitivity of0.15 R (3 σ). Complex distributions of ionized gas are revealed inthe nearby spiral arms up to 1-2 kpc away from the Galactic plane.Toward the inner Galaxy, the WHAM-NSS provides information about the WIMout to the tangent point down to a few degrees from the plane. Ionizedgas is also detected toward many intermediate velocity clouds at highlatitudes. Several new H II regions are revealed around early B starsand evolved stellar cores (sdB/O). This work presents the details of theinstrument, the survey, and the data reduction techniques. The WHAM-NSSis also presented and analyzed for its gross properties. Finally, somegeneral conclusions are presented about the nature of the WIM asrevealed by the WHAM-NSS.
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