Cometary Nebula Research Articles

The illumination of the GGD 30 nebulosity

An optical polarization map of the GGD 30 nebulosity shows that, although it shares many of the morphological characteristics of classical cometary nebulae such as NGC 2261/R.Mon, it differs in that the star-like knot at its head is not the illluminating and exciting source as previously assumed. The knot is reflection nebulosity and the true source, completely hidden from direct view at optical wave-lengths, is located some 6 arcsec east of the knot

The FU Orionis-type spectrum and bipolar outflow of Parsamyan 21

view Abstract Citations (34) References (31) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The FU Orionis--Type Spectrum and Bipolar Outflow of Parsamyan 21 Staude, H. J. ; Neckel, Th. Abstract We present CCD images in the red and long-slit spectrograms of the young cometary nebula Parsamyan 21. The spectroscopic and FIR properties of its illuminating source are characteristic for an FU Orionis star. The spectrum is of type F5Iab with broad absorption lines and a broad, blueshifted P Cygni profile of H-alpha, reaching a velocity of -600 km/s at the blue edge of its absorption component. The star coincides with a cold IRAS source and is associated with a short bipolar Herbig-Haro outflow oriented along the axis of symmetry of the cometary nebula. The image of the central source is nonstellar (FWHM = 1.20 arcsec) due to scattering by circumstellar dust. Publication: The Astrophysical Journal Pub Date: December 1992 DOI: 10.1086/172018 Bibcode: 1992ApJ...400..556S Keywords: Comets; Emission Spectra; H Alpha Line; Nebulae; Pre-Main Sequence Stars; Early Stars; Infrared Astronomy Satellite; Radio Jets (Astronomy); Astrophysics; ISM: JETS AND OUTFLOWS; ISM: INDIVIDUAL NAME: PARSAMYAN 21; STARS: PRE--MAIN-SEQUENCE full text sources ADS | data products SIMBAD (11)

The dynamics and physical properties of the cometary nebula G29.96 - 0.02

view Abstract Citations (33) References (22) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Dynamics and Physical Properties of the Cometary Nebula G29.96-0.02 Wood, Douglas O. S. ; Churchwell, Ed Abstract The H76-alpha recombination line emission distribution from the cometary UC H II regions G29.96 - 0.02 has been mapped with a resolution of 0.62 x 0.49 arcsec. The distribution of radial velocities in the ionized gas is well ordered. There is an unambiguous velocity gradient across the face of the nebula with velocities ranging from about 80 km/s on the leading edge of the cometary arc to about 105 km/s in the 'tail', a shift of about 25 km/s over an angular distance of about 4 arcsec. The linewidths are significantly broader along the leading edge of the cometary arc than elsewhere in the nebula. LTE electron temperatures are systematically low throughout the nebula, ranging from about 2500 K to 4200 K at different points in the H II region. Non-LTE line models combined with the continuum image imply that the electron densities in the arc are 5-10 times greater than in the tail of the nebula. G29.96 - 0.02 is moderately attenuated by interstellar dust. Publication: The Astrophysical Journal Pub Date: May 1991 DOI: 10.1086/169965 Bibcode: 1991ApJ...372..199W Keywords: Comets; Gas Dynamics; H Ii Regions; Interstellar Gas; Ionized Gases; Nebulae; Astronomical Models; Cosmic Dust; Radial Velocity; Spectral Emission; Spectral Line Width; Astrophysics; NEBULAE: INDIVIDUAL ALPHANUMERIC: G29.96-0.02; NEBULAE: INTERNAL MOTIONS; RADIO SOURCES: LINES full text sources ADS | data products SIMBAD (1)

The illumination of the cometary nebula 1548C27

Optical polarization maps of the crescent-shaped 1548C27 nebulosity show that there are two illuminating stars rather than the single apical one as previously assumed. The origin and nature of the jet is questioned.

Structure of Molecular Clouds Around some Pre-main Sequence Stars associated with Cometary Nebulae

AbstractWe present 12CO and 13CO molecular line observations of some pre-main sequence stars associated with cometary nebulae and attempt to unravel their detailed structure.

The illumination of the visible nebulosity in the L 810 dark cloud

A high-spatial-resolution polarization map of the visible nebulosity associated with the L810 dark cloud reveals that the dominant source of illumination and excitation is a star (L810 IRS) completely hidden from direct view at optical wavelengths, and is not the visible star # 7 as proposed by Neckel Th. & Staude H.J. . The five supposedly discrete cometary nebulae are also illuminated by the hidden source and do not have individual illuminationg stars.

On the connection between the IRAS point sources and galactic nonstable objects

The connection between the IRAS point sources catalog and following objects is studied: 1. H2O masers, 2. Herbig - Haro objects, 3. Cometary nebulae, 4. Compact nebulae, situated in the large nebulae, and 5. Dark globules. It is shown, that more than 50% of the 1, 2, 3, and 4 type objects are connected with the IRAS sources. More than 10 new H2O masers, connected with IRAS sources are found, one of them having very unusual properties. More than 10 dark globules are found in the Cep OB2 association, which are connected with IRAS sources. One of these sources consists of 4 components, forming a Trapezium-like configuration.

New Young Objects from the IRAS Point Source Catalogue

Three new objects have been found, when carrying out a survey of IRAS sources with colours like planetary nebulae, via low resolution spectroscopy. IRAS 14592-6311 and IRAS 07173-1733 are bright cometary nebulae, showing metal line emission very similar to V1331 Cyg (LkHα 120), which is the prototype of a certain number of T Tauri stars. They present strong P-Cygni profiles and some other peculiar characteristics. IRAS 14592-6311 is associated with a molecular cloud at a distance of 2.9 kpc, while IRAS 07173-1733 is located at the edge of the dark cloud KHAV 201. In the case of IRAS 05506+2414, it presents a bipolar structure with Herbig-Haro emission characteristics in one of the lobes, produces by shocked gas, and is located near Orion.

The nebula GM 1-27: A new case of directed outflow?

Investigation of the nebulous object GM 1-27 on the basis of direct photographs and spectra obtained with the 6-m telescope shows that it is a cometary nebula with mixed (C + E) spectrum. The high negative radial velocities of the lines (/minus/150 to /minus/200 km/sec) indicate a directed outflow of matter from the central star (which is not directly observable).

Bernes 48: An example of optically observed anisotropic outflow. I

The results are given of spectral investigation of the object Bernes 48 (RNO 129), which is an emission star with a very small cometary nebula. The star has spectral class G-K and has a moderately developed emission spectrum of T Tau type with conspicuous forbidden lines. The spectrum of the nebula differs from that of the star by a pronounced enhancement of the absorption lines of the Balmer series and reduction of all emissions. On the basis of the radial velocities, all the lines in the spectra of the star and the nebula can be divided into two systems, namely, all the allowed emission lines have a velocity of about +40 km/sec, while the forbidden emission lines and all absorption lines have one of about -140 km/sec. A preliminary phenomenological model of the object is proposed: a star with anisotropic ejection of matter and a bipolar nebula oriented almost along the line of sight.

A new cometary nebula in Cygnus

CCD images, surface polarimetry, and long-slit spectrograms of a hitherto unknown cometary reflection nebula associated with a dense dust cloud are presented. A bright, compact Herbig-Haro object is embedded in its brightest part. The highly reddened illuminating star of about 3-5 solar masses is located near the apex of the nebula; it emits a collimated bipolar high-velocity flow whose blueshifted component feeds the Herbig-Haro object. The redshifted component can be traced toward the interior of the dark cloud, where the density exceeds 100,000/cu cm. 20 references.

Polarimetry of the NGC 2261/R Monocerotis system and the faint jetlike feature to its southwest

Optical linear polarization maps of the region to the south of the NGC 2261/R Mon system show that the faint linear feature reported in 1985 by Walsh and Malin is reflection nebulosity directly illuminated by the star. The authors believe that it is the bright western rim of the highly obscured southern outflow from R Mon. The northern outflow, comprising the cometary nebula NGC 2261, shows polarization orientations that rotate with wavelength, deviating from the pattern expected in a simple reflection nebula. The authors offer an explanation involving an extensive magnetic field associated with the nebula and discuss the implications for magnetic acceleration of bipolar flows.

CCD observations of the counterfan in PV Cephei

view Abstract Citations (12) References (8) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS CCD Observations of the Counterfan in PV Cephei Levreault, Russell M. ; Opal, Chet B. Abstract Deep CCD images of PV Cephei reveal a faint, red "counterfan", opposite the star from the optically prominent fan previously known. This counterfan is clearly associated with the redshifted lobe of the PV Cephei molecular outflow, and its detection supports the contention that cometary nebulae are the optical counterparts of bipolar molecular outflows. The relative colors of the two halves of the optical nebulosity can be explained by differential reddening between the two lobes. Photometry of the gap between the stellar image and the bright optical fan is consistent with this gap being totally "black", indicating either high (≡4) values of AV due to a circumstellar disk or a total lack of material within the gap. Publication: The Astronomical Journal Pub Date: March 1987 DOI: 10.1086/114349 Bibcode: 1987AJ.....93..669L Keywords: Cepheid Variables; Charge Coupled Devices; Reflection Nebulae; Stellar Coronas; Stellar Mass Ejection; Brightness Distribution; Molecular Flow; Astrophysics; INTERSTELLAR: MATTER full text sources ADS | data products SIMBAD (2)

A Mechanism for Variability of Cometary Nebulae

A model is suggested to explain the variability of the optical structure and the integral brightness of cometary nebulae (CN) occurring at timescales of several years and tens of years (Gyulbudaghian et al. 1977, Cohen et al. 1977, 1981, Magakyan 1981, Gyulbudaghian 1982). A CN is assumed to be a reflection nebula; it is a wall of a conical cavity in the circumstellar gas-and-dust torus illuminated by the central star (Cohen 1974). I explain the CN's variability by the presence of small tilted circumstellar disc of gas-and-dust, located inside the internal channel of the large circumstellar torus (see Figure 1). A similar model was put forward by Ward-Thompson et al. (1985) to account for a tilt angle of about 30° between the direction of short optical jets (stellar wind, channelled by the small disc) and the large-scale bipolar outflow (focused by the large torus) in the CN NGC 6729 associated with the star R CrA. Tilt angles of about 30° between optical and radio structures exist in CN NGC 2261 (Cantó et al. 1981) and GM 1-29 (Levreault 1984).

Small Galactic Nebulae

We have performed high resolution VLA radio observations for several small H II regions, including the cluster emission nebulae S258, S255, S257, and S256. The region (PP56) between S255 and S257 at λ2 cm reveals significant flux structure close to OH, H2O and infrared emitting sources as shown in Figure 1. The flux densities and positions are indicated in Table 1. Observations of the cometary nebula PP59 (S269) also reveal similar characteristics as shown in Figure 2. These regions are considered to be active star-forming clouds. The cometary nebula PP40 was also observed and we note that its physical parameters are very similar to those of a typical planetary nebula.

The Star Formation Region Associated with the Cometary Nebula GM24

GM24 is a small visible nebulosity in the vicinity of a molecular cloud. In this contribution we present the results of continuum (6-cm) and CO line (J = 1 → 0) radio observations, infrared maps, broad-band photometry and low-resolution spectroscopy as well as long-slit Echelle Ha spectroscopy. We found evidence that the GM24 = PP85 nebula is part of a larger region where star formation occurred in the past 104 years; the region is embedded in a typical molecular cloud with a dimension of ∼ 10 pc and mass of ∼104 M⊙. A compact radio H II region seems to be associated with GM24 and with one of the mid-infrared peaks detected. The nebula is most probably the visible part of an embedded H II region that is starting to emerge from the cloud. The other infrared peaks found in its vicinity (∼ 1 pc) are probably associated with less evolved stellar objects. The complex also shows an extended near-infrared flux which we believe to arise in a reflection nebula. From energy arguments, we found that the luminosity required to power the H II region and keep the cloud at the observed large temperature (TK ≅33 K), is ∼105 L⊙ which is consistent with the infrared total flux from the present measurements and those from IRAS of 4x104 L⊙; this corresponds to the flux of ∼3 BO ZAMS stars. The details of the present work have appeared in the Revista Mexicana de Astronomía y Astrofísica, Volume 11, 83, 1985.

Shock excited emission knots in cometary reflection nebula

Near infrared and Ha CCD images of the newly found cometary reflection nebula GN 20.18.3. led to the discovery of its illuminating star and of a bright Ha knot located on its axis of symmetry. The knot has a Herbig-Haro spectrum indicating the presence of a collimated outflow from the central star. Also in the Bok globule L 810 a red CCD image reveals a cometary reflection nebula surrounding the central star, from which a shock excited filament is emanating. These observations emphasize the common origin of cometary nebulae and collimated high velocity flows.

Studies of small galactic nebulae

view Abstract Citations (16) References (17) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Studies of small galactic nebulae. Turner, K. C. ; Terzian, Y. Abstract High-resolution VLA radio observations are reported for several small H II regions, including the cluster emission nebulae S258, S255, S257, and S256. The region between S255 and S257 at λ2 cm reveals significant fine structure close to OH, H2O, and infrared emitting sources. Observations of the cometary nebula PP59(S269) also reveal similar characteristics. These regions are considered to be active star-forming clouds. The cometary nebula PP40 was also observed and it is suggested that it might be a planetary nebula. Publication: The Astronomical Journal Pub Date: January 1985 DOI: 10.1086/113708 Bibcode: 1985AJ.....90...59T Keywords: Milky Way Galaxy; Molecular Clouds; Nebulae; Radio Sources (Astronomy); Astronomical Maps; H Ii Regions; Planetary Nebulae; Radiant Flux Density; Stellar Evolution; Astrophysics full text sources ADS | data products SIMBAD (11)

A polarization study of the cometary nebula Parsamyan 21

La nebuleuse est relativement fortement polarisee et illuminee par l'etoile qu'elle contient. On observe une bande de polarisation qui peut etre due a des grains alignes dans un tore circumstellaire. Parsamyan 21 ressemble beaucoup, du point de vue de la polarisation, aux nebuleuses cometaires bien etudiees NGC 2261 et 6729, illuminees par R Mon et RGA respectivement

Investigation of the cometary nebula Parsamyan 21

The results are given of an isodensitometric and spectrophotometric investigation of the cometary nebula P 21 and its associated nucleus. The shape of the isodensities of the nucleus differs from those for normal stars, and in this the nucleus recalls R Mon. A spectral investigation of the nucleus of P 21 made on the basis of observations during 1981-1982 shows that it is a star of the class F2-F5V with an envelope expanding at about 120 km/sec.