Cometary Nebula Research Articles

The star in RNO 54: A possible post-FUor with a short faint jet

Aims. The aim of the present study is to analyze the spectra of an unusual pre-main sequence star in the cometary nebula RNO 54, which is suspected by several researchers to be a FUori-like object. Methods. We performed long-slit spectroscopy of the star using the 6m telescope with the SCORPIO-2 multi-mode focal reducer. Results. We discover a short (~4″ or ~6000 AU) and faint emission shock-excited jet from this star, probably oriented toward the long axis of the nebular ellipse. The spectral type of the star is estimated as G0-2 II; we confirm the split of the Li I absorption line, which is a typical sign indicating a FUori-like spectrum. Our analysis of the available data reveals an almost null photometric variability over at least the last 20 years. The lower limit of the bolometric luminosity of the star is estimated as 300 L⊙. Our study supports the classification of RNO 54 as a FUor-like star in the long post-outburst stage.

Spectral study of V565 Mon: probable FU Ori-like or chemically peculiar star

We present a detailed spectroscopic study of pre-main sequence star V565 Mon, which is the illuminating star of the Parsamian 17 cometary nebula. Observations were performed with the 2.6 m telescope in Byurakan Astrophysical Observatory on 2018 February 15. Radial velocities and equivalent widths of the most prominent lines of V565 Mon are presented. We build the spectral energy distribution and estimate the main parameters of the star, for example the obtained bolometric luminosity of V565 Mon is L V565 ≈ 130 L ⊙. Considering all features of V565 Mon, we come to the conclusion that this young intermediate-mass star belongs to some intermediate class between T Tau and HAeBe stars. Very unusual for a young star is the presence of strong absorption Ba II lines in the spectrum. Possible explanations on this issue are discussed. Hence, we think that V565 Mon is a unique example, which can help to understand some open questions involved in the problem of nucleosynthesis in young stars.

Condensations Expelled from the Stars, and Pairs of Stars, Connected with Bright Filaments

During several surveys of high-quality film-copies of the ESO B, R, ESO/SRC J, and EJ plates, except other young unstable objects (HH objects, star-forming regions, cometary nebulae) were found also two types of other unstable objects. 1. Bright condensations, connected with stars by bright filaments. 2. Pairs of stars, connected with each other by bright filaments. The objects of first type are mostly seen in infrared, on 2MASS K images. Due to their infrared colours, two of condensations and half of all stars can have thick dust discs.

Catalog of cometary nebulae and related objects (−42◦ < δ < +60◦)

The catalogue of cometary nebulae and related objects is compiled using the known up to the publication date lists.

Detections of Massive Stars in the Cluster MCM2005b77, in the Star-forming Regions GRS G331.34−00.36 (S62) and GRS G337.92−00.48 (S36)

Abstract Large infrared and millimeter wavelength surveys of the Galactic plane have unveiled more than 600 new bubble H ii regions and more than 3000 candidate star clusters. We present a study of the candidate clusters MCM2005b72, DBS2003−157, DBS2003−172, and MCM2005b77 based on near-infrared spectroscopy taken with SofI on the NTT and infrared photometry from the 2MASS, VVV, and GLIMPSE surveys. We find that (1) MCM2005b72 and DBS2003−157 are subregions of the same star-forming region, H ii GRS G331.34−00.36 (bubble S62). MCM2005b72 coincides with the central part of this H ii region, while DBS2003−157 is a bright mid-infrared knot of the S62 shell. We detected two O-type stars at extinction = 1.0–1.3 mag. Their spectrophotometric properties are consistent with the near-kinematic distance to GRS G331.34−00.36 of 3.9 ± 0.3 kpc. (2) DBS2003−172 coincides with a bright mid-infrared knot in the S36 shell (GRS G337.92−00.48), where we detected a pair of candidate He i stars embedded in a small cometary nebula. (3) The stellar cluster MCM2005b77 is rich in B-type stars, has an average of 0.91 mag, and is adjacent to the H ii region IRAS 16137−5025. The average spectrophotometric distance of ∼5.0 kpc matches the near-kinematic distance to IRAS 16137−5025 of 5.2 ± 0.1 kpc.

The Star Formation Regions SNO 76 and RCW 105

Two star formation regions in the southern sky are discussed. The first of these, SNO 76, consists of stars that form a trapezium system, along with IR stars and stars with dust envelopes. One of these stars is associated with a cometary nebula. This star is a variable with an amplitude of 3m.77. This system is associated with the point IR source IRAS 10138-6004. 12CO(1-0) observations of the molecular cloud associated with this star formation region reveal the presence of red and blue outflows. The second star formation region, RCW 105, consists of two groups of stars together with stars on bright filaments. These stars include IR stars and stars with dust envelopes. This star formation region is embedded in a radial system of type-I dark globules that is formed by the star HD 144969. This system is not included in any of the known catalogs of radial systems.

The Object CLN 138 – a Double Star-Formation Region

A double star formation region associated with the biconical cometary nebula CLN 138 is studied. 12CO(1-0) observations of a molecular cloud associated with this object reveal the existence of several molecular clouds in this region, as well as the existence of red and blue molecular outflows. Several new Herbig-Haro objects are found, two of which have undergone a luminosity increase of at least 8m. The first star formation region is basically embedded in the molecular cloud; most of the stars in it are infrared stars and many have dust envelopes. The second star formation region has already left the molecular cloud; it has no IR stars and few of its stars have dust clouds.

New Radial Systems of Dark Globules and HH Objects

During survey of ESO/SRC plates of the Southern Hemisphere, we have found several dozen new HH objects, star-forming regions, and cometary nebulae [1]. There are also radial systems of dark globules in the vicinity of these new objects. Several regions, containing some of these objects, were observed on the 1.54 m telescope with several narrow band filters. In this paper we present the results of observations of two new radial systems of dark globules and several HH objects and also the results of 12CO(1–0) observations of the dark cloud, part of which is rotating with angular velocity Ω = 4.3∙10−14 s−1.

DISCOVERY OF X-RAY PULSATIONS FROM THE INTEGRAL SOURCE IGR J11014–6103

We report the discovery of PSR J1101-6101, a 62.8 ms pulsar in IGR J11014-6103, a hard X-ray source with a jet and a cometary tail that strongly suggests it is moving away from the center of the supernova remnant (SNR) MSH 11-61A at v>1000 km/s. Two XMM-Newton observations were obtained with the EPIC pn in small window mode, resulting in the measurement of its spin-down luminosity E_dot = 1.36e36 erg/s, characteristic age Tau_c = 116 kyr, and surface magnetic field strength B_s = 7.4e11 G. In comparison to Tau_c, the 10-30 kyr age estimated for MSH 11-61A suggests that the pulsar was born in the SNR with initial period in the range 54 < P_0 < 60 ms. PSR J1101-6101 is the least energetic of the 15 rotation-powered pulsars detected by INTEGRAL, and has a high efficiency of hard X-ray radiation and jet power. We examine the shape of the cometary nebula in a Chandra image, which is roughly consistent with a bow shock at the velocity inferred from the SNR age and the pulsar's E-dot. However, its structure differs in detail from the classic bow shock, and we explore possible reasons for this.

Unstable Objects in Molecular Cloud LDN133

The results of investigation of molecular cloud LDN133 and the unstable objects HHL59, HHL59A, HHL59B and HHL59C connected with it are given. The IR nebula and IR star cluster are also connected with LDN133. It is shown that two different molecular outflows are present: (1) red-shifted molecular outflow from the IR nebula, connected with HHL59, and (2) bipolar molecular outflow from the object HHL59A. An IRAS point source IRAS 17554-2606 is connected with the IR nebula. Observations with narrow band filters revealed the existence of HH objects and jets from several unstable stars of this region. There are three filaments; ejected from the IR nebula with condensation at their ends. Two 8-type cometary nebulae connected with unstable stars were also discovered.

SERENDIPITOUS DISCOVERY OF AN INFRARED BOW SHOCK NEAR PSR J1549–4848 WITHSPITZER

We report on the discovery of an infrared cometary nebula around PSR J1549$-$4848 in our Spitzer survey of a few middle-aged radio pulsars. Following the discovery, multi-wavelength imaging and spectroscopic observations of the nebula were carried out. We detected the nebula in Spitzer IRAC 8.0, MIPS 24 and 70 $\mu$m imaging and in Spitzer IRS 7.5--14.4 $\mu$m spectroscopic observations, and also in the WISE all-sky survey at 12 and 22 $\mu$m.These data were analyzed in detail, and we find that the nebula can be described with a standard bow-shock shape, and that its spectrum contains polycyclic aromatic hydrocarbon and H$_2$ emission features. However, it is not certain which object drives the nebula. We analyze the field stars and conclude that none of them can be the associated object because stars with a strong wind or mass ejection that usually produce bow shocks are much brighter than the field stars. The pulsar is approximately 15\arcsec\ away from the region in which the associated object is expected to be located. In order to resolve the discrepancy, we suggest that a highly collimated wind could be emitted from the pulsar and produce the bow shock. X-ray imaging to detect the interaction of the wind with the ambient medium and high-spatial resolution radio imaging to determine the proper motion of the pulsar should be carried out, which will help verify the association of the pulsar with the bow shock nebula.

V2494 Cyg: a unique FU Ori type object in the Cygnus OB7 complex

A photometric and spectral study of the variable star V2494 Cyg in the L 1003 dark cloud is presented. The brightness of the star, formerly known as HH 381 IRS, increased by 2.5 mag in R (probably in the 1980s) and since then has remained nearly constant. Since the brightness increase, V2494 Cyg has illuminated a bipolar cometary nebula. The stellar spectrum has several features typical of the FU Ori type, plus it exhibits very strong Halpha and forbidden emission lines with high-velocity components. These emission lines originate in the HH jet near the star. The kinematic age of the jet is consistent with it forming at the time of the outburst leading to the luminosity increase. V2494 Cyg also produces a rather extended outflow; it is the first known FUor with both an observed outburst and a parsec-sized HH flow. The nebula, illuminated by V2494 Cyg, possesses similar morphological and spectral characteristics to Hubble's Variable Nebula (R Monocerotis/NGC 2261).

SHOCKED AND SCORCHED: THE TAIL OF A TADPOLE IN AN INTERSTELLAR POND

We report multi-wavelength observations of the far-infrared source IRAS 20324+4057, including high-resolution optical imaging with HST, and ground-based near-infrared, millimeter-wave and radio observations. These data show an extended, limb-brightened, tadpole-shaped nebula with a bright, compact, cometary nebula located inside the tadpole head. Our molecular line observations indicate that the Tadpole is predominantly molecular, with a total gas mass exceeding 3.7 Msun. Our radio continuum imaging, and archival Spitzer IRAC images, show the presence of additional tadpole-shaped objects in the vicinity of IRAS 20324+4057 that share a common E-W head-tail orientation: we propose that these structures are small, dense molecular cores that originated in the Cygnus cloud and are now being (i) photoevaporated by the ultraviolet radiation field of the Cyg OB2 No. 8 cluster located to the North-West, and (ii) shaped by ram pressure of a distant wind source or sources located to the West, blowing ablated and photoevaporated material from their heads eastwards. The ripples in the tail of the Tadpole are interpreted in terms of instabilities at the interface between the ambient wind and the dense medium of the former.

Two trapezium-type systems in CMa

This is an examination of two groups of stars, one of which contains a trapezium-type system consisting of four stars, while the second is made up of three stars, which are also part of a trapezium-type system. The two groups are located in the CMa OB1 association and contain cometary nebulae. Data on 12CO(1-0) observations of the molecular cloud connected with the first group of stars are presented. The central portion of the molecular cloud is moving toward us. This may be a consequence of the presence of a strong flow inside the cloud produced by the star-formation region.

Studies of a possible new Herbig Ae/Be star in the open cluster NGC 7380

We present a study of the star 2MASS J22472238+5801214 with the aim of identifying its true nature which has hitherto been uncertain. This object, which is a member of the young cluster NGC 7380, has been variously proposed to be a Be star, a D-type symbiotic and a Herbig Ae/Be star in separate studies. Here we present optical spectroscopy, near-IR photometry and narrow band Hα imaging of the nebulosity in its environment. Analysis of all these results, including the spectral energy distribution constructed from available data, strongly indicate the source to be a Herbig Ae/Be star. The star is found to be accompanied by a nebulosity with an interesting structure. A bow-shock shaped structure, similar to a cometary nebula, is seen very close to the star with its apex oriented towards the photoionizing source of this region (i.e. the star DH Cep). An interesting spectroscopic finding, from the forbidden [SII] 6716, 6731 Å and [OI] 6300 Å lines, is the detection of a blue-shifted high velocity outflow (200±50 km s−1) from the star.

ERUPTIVE VARIABLE STARS AND OUTFLOWS IN SERPENS NW

We study the outflow activity, photometric variability and morphology of three very young stellar objects in the Serpens NW star forming region: OO Serpentis, EC 37 (V370 Ser) and EC 53 (V371 Ser). High spatial resolution Keck/NIRC2 laser guide star adaptive optics images obtained in 2007 and 2009 in broad-band K and in a narrow-band filter centered on the 1-0 S(1) emission line of molecular hydrogen allow us to identify the outflows from all three objects. We also present new, seeing-limited data on the photometric evolution of the OO Ser reflection nebula and re-analyze previously published data. We find that OO Ser declined in brightness from its outburst peak in 1995 to about 2003, but that this decline has recently stopped and actually reversed itself in some areas of the reflection nebula. The morphology and proper motions of the shock fronts MHO 2218 near EC 37 suggest that they all originate in EC 37 and that this is an outflow seen nearly along its axis. We identify a molecular hydrogen jet emerging from the cometary nebula EC 53. The star illuminating EC 53 is periodically variable with a period of 543 days, and has a close-by, non-variable companion at a projected distance of 92 AU. We argue that the periodic variability is the result of accretion instabilities triggered by another very close, not directly observable, binary companion and that EC 53 can be understood in the model of a multiple system developing into a hierarchical configuration.

Southern YSO GRV10 and its environment

In this paper the southern cometary nebula GRV10 and its environment are investigated. The object is connected with a molecular cloud (its dimensions are ~4 pc). 12CO (1-0) observations toward GRV10 revealed the presence of two molecular outflows (a bipolar outflow), a red and a blue-shifted outflow, which coincide in position, indicating that they are moving along the line of sight in opposite directions. Near GRV10 a bright IR star, GRV10 IR, is discovered (near the southern edge of the nebula) and since its spectra and near IR colors favor it to be a Mira type star, a distance of ~4.4 kpc can be estimated. Star GRV10 IR appears connected with the IRAS point source IRAS 10406-6256. The grouping of stars (YSOs - young stellar objects) connected with GRV10 and embedded in a dark nebulosity is also discussed. This grouping is associated with the IRAS point source IRAS 10406-6253, which has FIR colors typical for embedded, not evolved, YSOs.

New Hα stars. Cyg OB7 region. I.

Preliminary results from a search for emission stars in the neighborhood of Cyg OB7 are reported. A new region of size 14×14 arc min lies 12 arc min to the south of HH 448. 17 new objects have been found, of which one is related to a nebula with an interesting shape and, apparently, the characteristics of a cometary nebula. Inside the nebula there are 4 faint, compact formations with very high proper motions. The spectrum of a star shows that it is of spectral class K9-M0 and is a T Tau type star at a distance of 220 pc. Most of the discovered stars with a strong or intermediate Ha emission line intensity are presumably also T Tau stars. This region appears to be a continuation of the T association around HH 448.

Search for HH-objects and emission stars in star formation regions. VI. Herbig-Haro objects and emission stars in the region of the GM 1-64 and GM 2-4 nebulae

Three new Herbig-Haro and 12 emission stars, mainly belonging to the T Tau class, have been discovered in a study of the region of the GM 1-64 and GM 2-4 nebulae in the direction of the galactic anticenter. GM 1-64 and GM 2-4 are typical cometary nebulae illuminated by emission stars. In GM 2-4 the central star is surrounded by a dense dust envelope and is observed only in the IR. Two stellar-like sources which are bright in the IR are found in this same region and can be regarded as young, Class 1 stars. One of them (CPM 19) is surrounded by a compact group of fainter PMS objects. It is found that CPM 19 shows up clearly in the optical range and undergoes large amplitude brightness variations.

Star formation and molecular clouds

The hypothesis advanced by V. A. Ambartsumyan according to which stars are formed from prestellar superdense objects-- protostars-- was an alternative to the hypothesis of the 1950's (and even now, not much changed) according to which stars are formed by accretion with subsequent collapse (in various modifications). Ambartsumyan's basic inferences were based on an analysis of the observational data available at that time. This paper presents both Ambartsumyan's pioneering ideas and some modern hypotheses of star formation. Some results from studies of molecular clouds and star formation regions are also discussed. One of the distinctive features of young stellar objects (YSO) is the outflow of matter from these objects (molecular, in the form of jets, etc.), a phenomenon whose importance for the evolution of stars was noted by Ambartsumyan as long ago as 1937. Radial systems of dark globules are examined, as well as H-H objects associated with star formation regions, cometary nebulae, and close Trapeziumtype systems (consisting of YSO).