Detection Of Radio Continuum Emission Research Articles

ASKAP-EMU Radio Emission from Type Ic Supernova SN1996aq in NGC 5584

We report the Australian Square Kilometre Array Pathfinder Evolutionary Map of the Universe survey detection of radio continuum emission from SN1996aq, a Type Ic supernova within the nearby face-on spiral galaxy NGC 5584. Analysis at multiple radio frequencies reveals radio emission coincident with SN1996aq. We find a flatter radio spectral index compared to the 2009 observations, indicating rapid evolution of SN1996aq. Conversely, no radio emission is observed from NGC 5584’s other known supernova, SN2007af. Furthermore, we identified two other significant radio continuum regions with properties consistent with H ii regions.

First Detection of Radio Emission Associated with a Classical Cepheid

We report the detection of 15 GHz radio continuum emission associated with the classical Cepheid variable star δ Cephei (δ Cep) based on observations with the Karl G. Jansky Very Large Array. Our results constitute the first probable detection of radio continuum emission from a classical Cepheid. We observed the star at pulsation phase ϕ ≈ 0.43 (corresponding to the phase of maximum radius and minimum temperature) during three pulsation cycles in late 2018 and detected statistically significant emission (>5σ) during one of the three epochs. The observed radio emission appears to be variable at a ≳10% level on timescales of days to weeks. We also present an upper limit on the 10 GHz flux density at pulsation phase ϕ = 0.31 from an observation in 2014. We discuss possible mechanisms that may produce the observed 15 GHz emission, but cannot make a conclusive identification from the present data. The emission does not appear to be consistent with originating from a close-in, late-type dwarf companion, although this scenario cannot yet be strictly excluded. Previous X-ray observations have shown that δ Cep undergoes periodic increases in X-ray flux during pulsation phase ϕ ≈ 0.43. The lack of radio detection in two out of three observing epochs at ϕ ≈ 0.43 suggests that either the radio emission is not linked with a particular pulsation phase, or else that the strength of the generated radio emission in each pulsation cycle is variable.

Radio properties of the OH megamaser galaxy IRAS 02524+2046

We present results from VLBI observations of continuum and OH line emission in IRAS 02524+2046 as well as arcsecond-scale radio properties of this galaxy using VLA archive data. We found that there is no significant detection of radio continuum emission from VLBI observations. The arcsecond-scale radio images of this source show no clear extended emission. The total radio flux density at L and C bands are approximately 2.9 mJy and 1.0 mJy, respectively, which indicates a steep radio spectral index between the two bands. A steep spectral index, low brightness temperature, and high q-ratio (i.e., the far-infrared to the radio flux density), which are three critical indicators in the classification of radio activity in the nuclei of galaxies, are all consistent with the classification of this source as a starburst galaxy from its optical spectrum. The high-resolution line profile reveals that we detected both the 1665 MHz and 1667 MHz OH maser lines, which show two and three clear components, respectively. The channel maps show that the maser emission are distributed in a region of ∼210 pc × 90 pc. The detected maser components in different regions indicate similar double spectral features, which might be evidence that this galaxy is at a stage of major merger as seen from the optical morphology.

Surveying the Giant H ii Regions of the Milky Way with SOFIA. I. W51A

Abstract We discuss the first results from our mid-infrared (MIR) imaging survey of Milky Way Giant H ii (GH ii) regions with our detailed analysis of W51A, which is one of the largest GH ii regions in our Galaxy. We used the FORCAST instrument on the Stratospheric Observatory For Infrared Astronomy (SOFIA) to obtain 20 and 37 μm images of the central 10′ × 20′ area, which encompasses both of the G49.5–0.4 and G49.4–0.3 subregions. Based on these new data, and in conjunction with previous multiwavelength observations, we conjecture on the physical nature of several individual sources and subcomponents within W51A. We find that extinction seems to play an important role in the observed structures we see in the near- to MIR, both globally and locally. We used the SOFIA photometry combined with Spitzer–IRAC and Herschel–PACS photometry data to construct spectral energy distributions (SEDs) of the subcomponents and point sources detected in the SOFIA images. We fit those SEDs with young stellar object models and found 41 sources that are likely to be massive young stellar objects, many of which are identified as such in this work for the first time. Close to half of the massive young stellar objects do not have detectable radio continuum emission at centimeter wavelengths, implying a very young state of formation. We derived luminosity-to-mass ratio and virial parameters of the extended radio subregions of W51A to estimate their relative ages.

High-mass Star Formation in the Outer Scutum–Centaurus Arm

Abstract The Outer Scutum–Centaurus (OSC) spiral arm is the most distant molecular spiral arm in the Milky Way, but until recently little was known about this structure. Discovered by Dame and Thaddeus, the OSC lies ∼15 kpc from the Galactic Center. Due to the Galactic warp, it rises to nearly 4° above the Galactic Plane in the first Galactic quadrant, leaving it unsampled by most Galactic plane surveys. Here we observe H ii region candidates spatially coincident with the OSC using the Very Large Array to image radio continuum emission from 65 targets and the Green Bank Telescope to search for ammonia and water maser emission from 75 targets. This sample, drawn from the Wide-field Infrared Survey Explorer Catalog of Galactic H ii Regions, represents every H ii region candidate near the longitude–latitude locus of the OSC. Coupled with their characteristic mid-infrared morphologies, detection of radio continuum emission strongly suggests that a target is a bona fide H ii region. Detections of associated ammonia or water maser emission allow us to derive a kinematic distance and determine if the velocity of the region is consistent with that of the OSC. Nearly 60% of the observed sources were detected in radio continuum, and more than 20% have ammonia or water maser detections. The velocities of these sources mainly place them beyond the Solar orbit. These very distant high-mass stars have stellar spectral types as early as O4. We associate high-mass star formation at 2 new locations with the OSC, increasing the total number of detected H ii regions in the OSC to 12.

Deep into the Water Fountains

(Abridged) The formation of large-scale (hundreds to few thousands of AU) bipolar structures in the circumstellar envelopes (CSEs) of post-Asymptotic Giant Branch (post-AGB) stars is poorly understood. The shape of these structures, traced by emission from fast molecular outflows, suggests that the dynamics at the innermost regions of these CSEs does not depend only on the energy of the radiation field of the central star. Deep into the Water Fountains is an observational project based on the results of programs carried out with three telescope facilities: The Karl G. Jansky Very Large Array (JVLA), The Australia Telescope Compact Array (ATCA), and the Very Large Telescope (SINFONI-VLT). Here we report the results of the observations towards the WF nebula IRAS 18043$-$2116: Detection of radio continuum emission in the frequency range 1.5GHz - 8.0GHz; H$_{2}$O maser spectral features and radio continuum emission detected at 22GHz, and H$_{2}$ ro-vibrational emission lines detected at the near infrared. The high-velocity H$_{2}$O maser spectral features, and the shock-excited H$_{2}$ emission detected could be produced in molecular layers which are swept up as a consequence of the propagation of a jet-driven wind. Using the derived H$_{2}$ column density, we estimated a molecular mass-loss rate of the order of $10^{-9}$M$_{\odot}$yr$^{-1}$. On the other hand, if the radio continuum flux detected is generated as a consequence of the propagation of a thermal radio jet, the mass-loss rate associated to the outflowing ionized material is of the order of 10$^{-5}$M$_{\odot}$yr$^{-1}$. The presence of a rotating disk could be a plausible explanation for the mass-loss rates estimated.

3.3 CM JVLA OBSERVATIONS OF TRANSITIONAL DISKS: SEARCHING FOR CENTIMETER PEBBLES

ABSTRACT We present sensitive (rms-noises ∼4–25 μJy) and high angular resolution (∼1″–2″) 8.9 GHz (3.3 cm) Karl G. Jansky Very Large Array radio continuum observations of 10 presumed transitional disks associated with young low-mass stars. We report the detection of radio continuum emission in 5 out of the 10 objects (RXJ1615, UX Tau A, LkCa15, RXJ1633, and SR 24s). In the case of LkCa15, the centimeter emission is extended, and has a similar morphology to that of the transitional disk observed at millimeter wavelengths with an inner depression. For these five detections, we construct the spectral energy distributions from the centimeter to submillimeter wavelengths, and find that they can be well fitted with a single (RXJ1633 and UX Tau A) or a two-component power law (LkCa15, RXJ1615, and SR 24s). For the cases where a single power law fits the data well, the centimeter emission is likely produced by optically thin dust with large grains (i.e., centimeter-size pebbles) present in the transitional disks. For the cases where a double power law fits the data, the centimeter emission might be produced by the combination of photoevaporation and a free–free jet. We conclude that RXJ1633 and UX Tau A are excellent examples of transitional disks where the structure of the emission from centimeter/millimeter pebbles can be studied. In the other cases, some other physical emitting mechanisms are also important in the centimeter regime.

A multi-wavelength study of a double intermediate-mass protostar – from large-scale structure to collimated jets

Aims. The earliest stages of intermediate- and high-mass star for mation remain poorly understood. To gain deeper insights, we study a previously discovered protostellar source that is deeply embedded and drives an energetic molecular outflow. Methods. The source, UYSO 1, located close to IRAS 07029‐1215 at a distance of about 1 kpc, was observed in the (sub)millimeter and centimeter wavelength ranges, as well as at near-, mid-, and far-infrared wavelengths. Results. The multi-wavelength observations resulted in the detection of a double intermediate-mass protostar at the location of UYSO 1. In addition to the associated molecular outflow, with a projected size of 0.25 pc, two intersecting near-infrared jets with projected sizes of 0.4 pc and 0.2 pc were found. However, no infrared counterparts to the driving sources could be detecte d in sensitive near- to far-infrared observations (including Spitzer ). In interferometric millimeter observations, UYSO 1 was resolved into two continuum sources with high column densities (> 10 24 cm −2 ) and gas masses of 3.5 M⊙ and 1.2 M⊙, with a linear separation of 4200 AU. We report the discovery of a H2O maser towards one of the two sources. Within an appropriate multi-wavelength coverage, the total luminosity is roughly estimated to be≈50 L⊙, shared by the two components, one of which is driving the molecular outflow that has a dynamical timescale of less than a few thous and years. The jets of the two individual components are not aligned. Submillimeter observations show that the region lacks the typical hot-core chemistry. Conclusions. We find two protostellar objects, whose associated circumst ellar and parent core masses are high enough to suggest that they may evolve into intermediate-mass stars. This is corroborated by their association with a very massive and energetic CO outflow, suggesting high protostellar accretion rates. The short dynamical timescale of the outflow, the pristine chemi cal composition of the cloud core and absence of hot core tracers, the absence of detectable radio continuum emission, and the very low protostellar luminosity argue for an extremely early evolutionary stage.

HiImaging Observations of Superthin Galaxies. I. UGC 7321

We have used the Very Large Array to image the isolated superthin galaxy UGC 7321 in the H I line with a spatial resolution of 16'' and a spectral resolution of 24 kHz (5.2 km s-1). We have reached a sensitivity of (0.36–0.40) mJy beam-1 channel-1, which correspond to a column density of (8–9) × 1018 atoms cm-2 (1 σ). UGC 7321 has a gas-rich disk, with MH I = (1.06 ± 0.01) × 109 d M⊙ and MH I/LB = 1.0 (d10 is the distance to UGC 7321 in units of 10 Mpc, the value adopted in this paper), and no detectable radio continuum emission (FCONT = 0.41 ± 0.25 mJy). The global H I distribution of UGC 7321 is rather symmetric and extends to ~1.5 times the optical radius (DH I = 865 ± 015 at nH I = 3 × 1019 atoms cm-2). An integral sign warp is observed in the H I disk, commencing near the edge of the stellar distribution and twisting back toward the equatorial plane in the outermost regions. In addition, the position-velocity diagram suggests the presence of a bar or inner arm within ~40'' from the center. The rotation curve of UGC 7321 is slowly rising; it reaches its asymptotic velocity of ~110 km s-1 at ~25 from the center (about 0.9 optical radii) and declines near the edge of the H I disk. The ratio of the inferred dynamical mass to the mass in gas and stars is ~12d, implying that UGC 7321 is a highly dark-matter–dominated galaxy.

Mid-infrared observations of methanol maser sites and ultracompact H ii regions: signposts of high-mass star formation

N-band (10.5 μm) and/or Q-band (20.0 μm) images taken with MANIAC on the ESO/MPI 2.2-m telescope are presented for 31 methanol maser sites and 19 ultracompact (UC) H ii regions. Most of the maser sites and UC H ii regions are coincident with mid-infrared (MIR) sources to within the positional uncertainties of ∼ 3 arcsec, consistent with the maser emission being powered by the MIR source. The IRAS source positions, however, do not always coincide with the MIR sources. Based on an average infrared spectral energy distribution, we deduce that the MIR objects are luminous enough that they should also produce a strong ionizing radiation. Some sources are consistent with stars of later spectral type, but not all can be. A number of maser sites show no detectable radio continuum emission associated with MIR emission, despite a powering source luminous enough potentially to produce an UC H ii region. Since no signs of an UC H ii region are detected here, these maser sites might be produced during a very early stage of stellar evolution. We present objects that show evidence of outflow activity stemming from a maser site, exhibiting CO and/or CS line profiles indicative of outflows coincident with the MIR source. These cases are promising examples of maser sites signposting the earliest stages of high-mass star formation.

A molecular-line study of clumps with embedded high-mass protostar candidates

We present molecular line observations made with the IRAM 30-m telecopes of the immediate surroundings of a sample of 11 candidate high-mass protostars. These observations are part of an effort to clarify the evolutionary status of a set of objects which we consider to be precursors of UC HII regions. In a preceding series of papers we have studied a sample of objects, which on the basis of their IR colours are likely to be associated with compact molecular clouds. The original sample of 260 objects was divided approximately evenly into a High group, with IR colour indices [25-12] ≥ 0.57 and [60-12] ≥ 1.3, and a Low group with complementary colours. The FIR luminosity of the Low sources, their distribution in the IR colour-colour diagram, and their lower detection rate in H_2O maser emission compared to the High sources, led to the hypothesis that the majority of these objects represent an earlier stage in the evolution than the members of the High group, which are mostly identifiable with UC HII regions. Subsequent observations led to the selection of 12 Low sources that have FIR luminosities indicating the presence of B2.5 to O8.5 V0 stars, are associated with dense gas and dust, have (sub-)mm continuum spectra indicating temperatures of ~30 K, and have no detectable radio continuum emission. One of these sources has been proposed by us to be a good candidate for the high-mass equivalent of a Class 0 object. In the present paper we present observations of the molecular environment of 11 of these 12 objects, with the aim to derive the physical parameters of the gas in which they are embedded, and to find further evidence in support of our hypothesis that these sources are the precursors to UC HII regions. We find that the data are consistent with such an interpretation. All observed sources are associated with well-defined molecular clumps. Masses, sizes, and other parameters depend on the tracer used, but typically the cores have average diameters of ~0.5-1 pc (with a range of 0.2 to 2.2 pc), and masses of a few tens to a few thousand solar masses. Compared to a similar analysis of High sources, the present sample has molecular clumps that are more massive, larger, cooler, and less turbulent. They also tend to have a smaller ratio of virial-to-luminous mass, indicating they are less dynamically stable than their counterparts in which the High sources are embedded. The large sizes suggest these clumps should still undergo substantial contraction (their densities are ~10 times smaller than those of the High sources). The lower temperatures and small linewidths are also expected in objects in an earlier evolutionary state. In various sources indications are found for outflowing gas, though its detection is hampered by the presence of multiple emission components in the line spectra. There are also signs of self-absorption, especially in the spectra of ^(13)CO and HCO+. We find that the masses of the molecular clumps associated with our objects increase with L_(fir) (M_(clump) ∝ L^(1.17)_(fir)), and that there is a (weak) relation between the clump mass and the mass of the embedded protostellar object M_(proto) ∝ M^(0.30)_(clump). The large amount of observational data is necessarily presented in a compact, reduced form. Yet we supply enough information to allow further study. These data alone cannot prove or disprove the hypothesis that among these objects a high-mass protostar is truly present. More observations, at different wavelenghts and spatial resolutions are needed to provide enough constraints on the number of possible interpretations.

Mid‐Infrared Imaging of Star‐forming Regions Containing Methanol Masers

We present a mid-infrared imaging survey of 21 sites of massive star formation associated with methanol masers. Images were obtained from the Cerro Tololo Inter-American Observatory 4 m Blanco telescope using the University of Florida imager/spectrometer OSCIR. Of the 10 sites where the methanol masers are distributed in a linear fashion, we find three sources that are elongated at the same position angle as their linear methanol maser distributions. It is believed that these elongated mid-infrared objects are indeed circumstellar disks. It was found that the masers may arise inside the mid-infrared emitting regions of these young stellar objects, indicating that the methanol masers may be pumped by mid-infrared photons. Many mid-infrared sources in our survey have no detectable radio continuum emission, and we advance the hypothesis that these sources are lower mass, nonionizing stars.

AVLA search for embedded young stellar objects and protostellar candidates in L1630

Five molecular cloud cores in L1630 have been observed with the VLA in C configuration at a wavelength of 3.5 cm. These cores were identified in molecular line emission by a previous study, and contain numerous clumps which are excellent candidates for sites of low-mass star formation. To a 5σ limit of 0.1 mJy, corresponding to an 8.4-GHz luminosity of 1.9 × 1016 erg s−1 Hz−1 (uncorrected for primary beam attenuation), most (>75 per cent) of the clumps within these cores do not have an associated radio continuum source. Of the three likely associations, two were discovered in previous surveys of LBS 23 (HH 24–26), one of which (SSV 61) shows evidence for radio variability, while the third source is spatially coincident with one of the clumps in LBS 18 and may be a new class 0 protostar candidate. Another new discovery is that HH 26IR is probably detected at the 4σ level. Radio emission has also been detected from two of the early-type stars exciting the NGC 2068 reflection nebula (HD 38563C and S). These results are in agreement with earlier work which proposes that, in (the northern part of) L1630, a large fraction of the molecular gas is not directly involved with star formation at the current epoch, although there is evidence that low-mass star formation is in the early stages at a number of locations. A tentative suggestion is that perhaps only young stellar objects in the earliest and latest phases of protostellar evolution exhibit detectable radio continuum emission. The earliest emission may be due to bremsstrahlung from an ionized jet, which declines as a result of a decreasing accretion rate or outflow efficiency. The later emission is due to gyrosynchrotron processes arising as a consequence of a magnetic field in the vicinity of the star—disc interface. Alternatively, a combination of the source geometry and optical depth may be responsible for such an apparent correlation. Further observations of a larger sample are required to test whether this correlation is seen in a wider view of low-mass star formation.

Detection of radio continuum emission from circumstellar dust around CRL 2688 and IRC +10216

view Abstract Citations (26) References (27) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Detection of Radio Continuum Emission from Circumstellar Dust around CRL 2688 and IRC +10216 Knapp, G. R. ; Bowers, P. F. ; Young, K. ; Phillips, T. G. Abstract We report the detection by the VLA of continuum emission at 8.4 GHz (3.6 cm) from the evolved carbon stars CRL 2688 and IRC +10216. The emission from CRL 2688 extends at least 15 sec (2 x 1017 cm at 1 kpc distance) from the star. Comparison with the infrared and submillimeter flux shows that the likeliest mechanism is emission from warm circumstellar dust; if so, the dust emissivity is high at wavelengths well into the radio regime; the best-fit long-wavelength power-law exponent is beta is approximately 0.8. This high emissivity shows that the dust has amorphous or layered structure and also offers the possibility of mapping the distribution of matter in circumstellar envelopes at high angular resolution at wavelengths where the emission is optically thin. Publication: The Astrophysical Journal Pub Date: July 1994 DOI: 10.1086/187406 Bibcode: 1994ApJ...429L..33K Keywords: Asymptotic Giant Branch Stars; Carbon Stars; Continuous Radiation; Cosmic Dust; Emission Spectra; Radio Astronomy; Stellar Envelopes; Stellar Mass; Stellar Radiation; Stellar Spectra; Submillimeter Waves; Infrared Astronomy; Very Large Array (Vla); Astronomy; STARS: AGB AND POST-AGB; STARS: CARBON; STARS: INDIVIDUAL ALPHANUMERIC: CRL 2688; STARS: INDIVIDUAL ALPHANUMERIC: IRC; 10216; STARS: MASS LOSS full text sources ADS | data products SIMBAD (2)

Detection of radio continuum emission from Procyon

view Abstract Citations (35) References (29) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Detection of Radio Continuum Emission from Procyon Drake, Stephen A. ; Simon, Theodore ; Brown, Alexander Abstract We have detected the F5 IV-V star Procyon as a weak and variable 3.6 cm radio continuum source using the VLA. The inferred radio luminosity is similar to, though some-what higher than, the X-band luminosity of the active and flaring sun. The 33 micro-Jy flux density level at which we detected Procyon on four of five occasions is close to the 36 micro-Jy radio flux density expected from a model in which the radio emission consists of two components: optically thick 'stellar disk' emission with a 3.6 cm brightness temperature of 20,000 K that is 50 percent larger than the solar value, and optically thin coronal emission with an emission measure the same as that indicated by Einstein and EXOSAT X-ray flux measurements in 1981 and 1983. The maximum mass-loss rate of a warm stellar wind is less than 2 x 10 exp -11 solar mass/yr. An elevated flux density of 115 micro-Jy observed on a single occasion provides circumstantial evidence for the existence of highly localized magnetic fields on the surface of Procyon. Publication: The Astrophysical Journal Pub Date: March 1993 DOI: 10.1086/172436 Bibcode: 1993ApJ...406..247D Keywords: Continuous Radiation; Dwarf Stars; Radio Emission; Stellar Luminosity; Stellar Radiation; Nonthermal Radiation; Very Large Array (Vla); Astrophysics full text sources ADS | data products SIMBAD (3)

Radio Continuum Observations of Southern Planetary Nebulae Candidates

In an attempt to find new Planetary Nebulae we have short radio continuum observations at 6 cm and 3 cm of 90 PN candidates with the Australian Compact Array. We selected the unidentified objects from the IRAS Point Source Catalogue on basis of their PN colors. Detection of radio continuum emission at the IRAS position almost certainly confirms that these objects are PN, because it indicates the presence of ionized gas. Therefore the 18 detected sources are considered new PN. Because of their high brightness temperatures, they are probably young PN.

Radio continuum emission from young stellar objects in L1641

view Abstract Citations (32) References (31) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Radio Continuum Emission from Young Stellar Objects in L1641 Morgan, James A. ; Snell, Ronald L. ; Strom, Karen M. Abstract The results of a 6 and 20 cm radio continuum survey of young stellar objects in the L1641 region located south of the Orion Nebula are presented. Four are identified as low-luminosity young stellar objects in L1641 and three more as Herbig-Haro or Herbig-Haro-like objects. These objects have bolometric luminosities between 80 and 300 solar, and their 6-20 cm spectral index suggests optically thick, free-free emission. They are characterized by a rising spectrum between 2.2 and 25 microns, have no optical counterparts, and are associated with stellar wind activity. Thus, detectable radio continuum emission may be produced only by the youngest and most luminous objects in L1641. Publication: The Astrophysical Journal Pub Date: October 1990 DOI: 10.1086/169264 Bibcode: 1990ApJ...362..274M Keywords: Continuous Radiation; Early Stars; Orion Nebula; Pre-Main Sequence Stars; Radio Emission; Stellar Radiation; Extragalactic Radio Sources; Herbig-Haro Objects; Stellar Luminosity; Stellar Winds; Astrophysics; NEBULAE: INDIVIDUAL ALPHANUMERIC: L1641 (LYNDS 1641); STARS: PRE--MAIN-SEQUENCE; STARS: RADIO RADIATION full text sources ADS | data products SIMBAD (58)

Detection of radio continuum emission from Herbig-Haro objects 1 and 2 and from their central exciting source

The region in Orion containing HH 1 and HH 2 was observed with the VLA at 20, 6, and 2 cm on several occasions from 1981 to 1984. At lower resolution, four continuum sources were detected. Two of these sources coincide positionally with HH 1 and HH 2. At 6 cm and higher resolution, HH 1 is resolved into at least two components. The emission is probably bremsstrahlung originating in the same region where the visible line emission is produced. This is the first detection of radio continuum from classic Herbig-Haro objects. At a position closely centered between HH 1 and HH 2, an object that can be interpreted as the energy source of the system was detected. The central source spectrum is S(nu) of about nu to the alpha power, where alpha = 0.4 + or - 0.2, suggesting a stellar wind. Finally, the fourth radio continuum source coincides positionally with an H2O maser and is probably excited by an independent star. There is evidence of time variability in its radio flux. No emission was detected from the Cohen-Schwartz (1979) star at the 0.1 mJy level.

Radio Continuum Interferometry of Dark Clouds - Part Two - a Study of the Physical Properties of Local Newly Formed HII Regions

A radio continuum survey of dark clouds (Gilmore 1980a) revealed only a few new regions of star formation. The observations of these individual regions are presented and discussed in this paper. The regions include S140 IR, S156, and Mon R2, as well as the dark cloud complexes in Perseus, Taurus, Orion, and Ophiuchus. The H II regions detected in the radio continuum have associated visible nebulosity and are excited by early B stars. However, five infrared sources thought to have the luminosity of early B stars were not detected in the radio continuum. These five sources showed high correlation with the presence of CO self-absorption, CO emission over a wide range of velocities, and type I OH masers, but an absence of coincident visible nebulosity and detectable radio continuum emission. Therefore, it is suggested that they represent an earlier evolutionary stage than those H II regions detected in the radio continuum. This first evolutionary state marks the presence of "pre-emergent" (with respect to the molecular cloud) cocoon stars. H II regions in the second evolutionary state are marked by the presence of detectable radio continuum emission, i.e., they are stronger than 10 mJy at 2695 MHz. They have associated visible nebulosity, are relatively large, and appear to be located at the edges of molecular clouds. We designate these as "emergent edge" H II regions. The fact that many young H II regions are edge H II regions implies that massive stars may be born near the edges of clouds, a phenomenon previously suggested by several other investigators. Comparison of the results of this survey with other investigators of H II regions and newly formed massive stars indicates that the radio continuum detectability of H II regions surrounding young massive cocoon stars is a function of the age and mass of the star. 09.5 ZAMS stars and earlier types may exhibit detectable radio continuum emission before the cocoon reaches the edge of a cloud and breaks up into a core/halo-type of object. BO ZAMS stars may exhibit characteristics of both evolutionary states.

Far-infrared emission from compact sources in NGC 2264 and the Rosette Nebula

view Abstract Citations (79) References (20) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Far-infrared emission from compact sources in NGC 2264 and the Rosette nebula. Harvey, P. M. ; Campbell, M. F. ; Hoffmann, W. F. Abstract The paper reports the discovery of far-IR emission at 53, 100, and 175 microns from two sources (one in NGC 2264 and another near the Rosette Nebula) associated with molecular clouds but not with any detectable radio continuum emission. The maximum source diameters are estimated to be 20 arcsec, and the spectra of both objects are shown to be broader than that of a 'typical' H II region. It is found that both objects are unresolved at all the IR wavelengths observed, have relatively wide IR spectra, are located at or near the apices of fan-shaped cometary nebulae, have colors between 50 and 200 microns that are among the coolest of any observed far-IR sources, and have luminosities that are an order of magnitude less than the weakest sources observed near compact H II regions. A cylindrically symmetric source model is considered in which a 'hole' in the dust distribution around the central source provides the visible luminosity of the nearby nebula and the dust temperature decreases rapidly with distance. It is suggested that the central sources are probably pre-main-sequence stellar objects with masses of 5 to 10 solar masses and luminosities of a few thousand suns. Publication: The Astrophysical Journal Pub Date: July 1977 DOI: 10.1086/155341 Bibcode: 1977ApJ...215..151H Keywords: Far Infrared Radiation; Infrared Astronomy; Nebulae; Continuous Radiation; H Ii Regions; Infrared Spectra; Optical Thickness; Spectral Energy Distribution; Stellar Evolution; Astrophysics full text sources ADS |