A Herbig–Haro object associated with GGD30 and its exciting source

GGD30 has been suggested to be either a small reflection nebulosity or a Herbig–Haro (HH) object formed in the outflow from a nearby obscured star. Observations to date have not been able to distinguish between these two scenarios. In addition, there are conflicting proposals for the location of the exciting source for GGD30. To resolve these questions, we have carried out optical spectroscopy and near-infrared ( J , K and 3.6-μm) imaging of GGD30. Taken together, these observations reveal that the bright optical knot in GGD30 must be a HH object, excited by the outflow from an optically obscured pre-main-sequence (PMS) star located ∼3 arcsec to the southwest. Based on mid-infrared fluxes from the Mid-course Space Experiment ( MSX ) satellite, we estimate the luminosity of this PMS star to be  ∼12.5 L_⊙  which suggests it is an intermediate-mass object rather than low-mass as previously proposed. The optical spectroscopy indicates projected velocities of  ∼−270 km s⁻¹  associated with the HH object. The fact that these velocities are blueshifted and relatively high compared to the velocities typical of HH flows suggests that the outflow from the PMS star must be almost aligned with the line of sight. There is an additional low-velocity  (∼−70 km s⁻¹) Hα  component but its origin is not clear.     

New, high-resolution, near-infrared observations of HH 1

We present new, high-resolution, near-infrared images of the HH 1 jet and bow shock. H₂ and [Fe  ii ] images are combined to trace excitation changes along the jet and across the many shock features in this flow. Echelle spectra of H₂ profiles towards a few locations in HH 1 are also discussed. Gas excitation in oblique, planar C-type shocks best explains the observations, although J-type shocks must be responsible for the observed [Fe  ii ] emission features. Clearly, no single shock model can account for all of the observations. This will probably be true of most, if not all, Herbig–Haro flows.     

The excitation and kinematical properties of H2 and [Fe ii] in the HH 46/47 bipolar outflow

Long-slit spectra of the molecular outflow Herbig–Haro (HH) 46/47 have been taken in the J and K near-infrared bands. The observed H₂ line emission confirms the existence of a bright and extended redshifted counter-jet outflow south-west of HH 46. In contrast with the optical appearance of this object, we show that this outflow seems to be composed of two different emission regions characterized by distinct heliocentric velocities. This implies an acceleration of the counter-jet.
The observed [Fe  ii ] emission suggests an average extinction of 7–9 visual magnitudes for the region associated with the counter-jet.
Through position–velocity diagrams, we show the existence of different morphologies for the H₂ and [Fe  ii ] emission regions in the northern part of the HH 46/47 outflow. We have detected for the first time high-velocity (−250 km s⁻¹) [Fe  ii ] emission in the region bridging HH 46 to HH 47A. The two strong peaks detected can be identified with the optical positions B8 and HH 47B.
The H₂ excitation diagrams for the counter-jet shock suggest an excitation temperature for the gas of T _ex≈2600 K . The lack of emission from the higher energy H₂ lines, such as the 4–3 S(3) transition, suggests a thermal excitation scenario for the origin of the observed emission. Comparison of the H₂ line ratios with various shock models yielded useful constraints about the geometry and type of these shocks. Planar shocks can be ruled out whereas curved or bow shocks (both J- and C-type) can be parametrized to fit our data.     

A burst of outflows from the Serpens cloud core: wide-field submillimetre continuum, CO J=2–1 and optical observations

Wide-field mapping of Serpens in submillimetre continuum emission and CO J =2–1 line emission is here complemented by optical imaging in [S  ii ] λλ 6716, 6731 line emission. Analysis of the 450- and 850-μm continuum data shows at least 10 separate sources, along with fainter diffuse background emission and filaments extending to the south and east of the core. These filaments describe 'cavity-like' structures that may have been shaped by the numerous outflows in the region. The dust opacity index, β , derived for the identifiable compact sources is of the order of 1.0±0.2, with dust temperatures in excess of 20 K. This value of β is somewhat lower than for typical class I YSOs; we suggest that the Serpens sources may be 'warm', late class 0 or early class I objects.
With the combined CO and optical data we also examine, on large scales, the outflows driven by the embedded sources in Serpens. In addition to a number of new Herbig–Haro flows (here denoted HH 455–460), a number of high-velocity CO lobes are observed; these extend radially outwards from the cluster of submillimetre sources in the core. A close association between the optical and molecular flows is also identified. The data suggest that many of the submillimetre sources power outflows. Collectively, the outflows traced in CO support the widely recognized correlation between source bolometric luminosity and outflow power, and imply a dynamical age for the whole protostellar cluster of ∼3×10⁴ yr. Notably, this is roughly equal to the proposed duration of the 'class 0' stage in protostellar evolution.     

A shallow though extensive H2 2.122-μm imaging survey of Taurus–Auriga–Perseus – I. NGC 1333, L1455, L1448 and B1

We discuss wide-field near-infrared (near-IR) imaging of the NGC 1333, L1448, L1455 and B1 star-forming regions in Perseus. The observations have been extracted from a much larger narrow-band imaging survey of the Taurus–Auriga–Perseus complex. These H₂ 2.122-μm observations are complemented by broad-band K imaging, mid-IR imaging and photometry from the Spitzer Space Telescope , and published submillimetre CO   J = 3–2  maps of high-velocity molecular outflows. We detect and label 85 H₂ features and associate these with 26 molecular outflows. Three are parsec-scale flows, with a mean flow lobe length exceeding 11.5 arcmin. 37 (44 per cent) of the detected H₂ features are associated with a known Herbig–Haro object, while 72 (46 per cent) of catalogued HH objects are detected in H₂ emission. Embedded Spitzer sources are identified for all but two of the 26 molecular outflows. These candidate outflow sources all have high near-to-mid-IR spectral indices (mean value of  α∼ 1.4  ) as well as red IRAC 3.6–4.5 μm and IRAC/MIPS 4.5–24.0 μm colours: 80 per cent have [3.6]–[4.5] > 1.0 and [4.5]–[24] > 1.5. These criteria – high α and red [4.5]–[24] and [3.6]–[4.5] colours – are powerful discriminants when searching for molecular outflow sources. However, we find no correlation between α and flow length or opening angle, and the outflows appear randomly orientated in each region. The more massive clouds are associated with a greater number of outflows, which suggests that the star formation efficiency is roughly the same in each region.     

Chemical evolution ahead of Herbig–Haro objects

Compact regions of enhanced HCO⁺ and NH₃ emission have been detected close to a number of Herbig–Haro objects. An interpretation of these detections is the following: a transient clump within the molecular cloud has been irradiated by the shock that generates the Herbig–Haro object. The irradiation releases icy mantles from the grains within the transient clump and initiates a photochemistry. On the basis of this picture, we have developed an extensive chemical model which predicts that a wide range of species, other than NH₃ and HCO⁺, should also be detectable. These include CH₃OH, H₂S, C₃H₄, H₂CO, SO, SO₂, H₂CS and NS. The chemical effects should last ∼  10⁴ yr  .     

The birth of a planetary nebula around the carbon star IRC+10216

Our current understanding of the evolution of solar-type stars suggests that after a period as a red giant star, during which mass loss occurs continuously in the form of a stellar wind, a period of intense mass loss known as a superwind occurs, during which a significant fraction of the envelope of the star is ejected into space, forming the material from which a planetary nebula (PN) will be constructed. It has been suggested that this superwind ejects material from the star in a toroidal or disc-like fashion, rather than isotropically. Here we present Hubble Space Telescope optical images of a toroidal superwind caught in the act: our images of the carbon star IRC+10216, which is believed to be in the final stages of red giant evolution, show that most of its optical emission is a bipolar reflection nebula. We show that the full spectral energy distribution and these images can be modelled as an equatorially enhanced dusty superwind, providing the first direct observational support for the toroidal superwind model, and supporting the 'interacting winds' model of PN formation.     

A large radio nebula around P Cygni

We present a large set of radio observations of the luminous blue variable P Cygni. These include two 6-cm images obtained with MERLIN which spatially resolve the 6-cm photosphere, monitoring observations obtained at Jodrell Bank every few days over a period of two months, and VLA observations obtained every month for seven years. This combination of data shows that the circumstellar environment of P Cyg is highly inhomogeneous, that there is a radio nebula extending to almost an arcminute from the star at 2 and 6 cm, and that the radio emission is variable on a time-scale no longer than one month, and probably as short as a few days. This short-time-scale variability is difficult to explain. We present a model for the radio emission with which we demonstrate that the star has probably been losing mass at a significant rate for at least a few thousand years, and that it has undergone at least two major outbursts of increased mass loss during the past two millenia.     

年轻星天体喷流的近红外成像观测进展

分子氢的红外振动发射线是显现年轻星质量外流的重要谱线之一。自Gautier等人1976年在猎户座发现年轻星质量外流的分子氢发射开始,人们在银河系内几乎所有的恒星形成区都发现了这种线发射。研究表明,分子氢发射与年轻星周围的其它活动现象（如分子外流和光学喷流）之间有着非常密切的联系。红外和光学喷流代表了年轻星剧烈活动的两个侧面,是喷流与周围介质相互作用强弱不同的表现,这种作用还拖带周围介质,产生分子外流,光学、红外喷流和分子外流组成了恒星形成区壮观的景象,它们是恒星形成活动的重要标志。随着红外探测技术的飞速发展,对年轻星外流活动现象的观测越来越丰富的详细,使人们对这种现象的本质越来越了解。在20世纪90年代NICMOS等大阵列红外探测器投入使用后,红外成像观测有了长足的进步。目前已在70个左右的区域里发现了H2发射,这一数字还在迅速增加,今后的研究主要可能向两个方向发展。其一是高分辨观测,进一步了解H2发射的结构以及与光学喷流和分子外流之间的关系;其二是天观测,了解银河系内的恒星形成H2区发射的大尺度结构和恒星形成的统计分布规律。     

Is LkHα 264 like a young, extremely active Sun?

We combine calibrated International Ultraviolet Explorer ( IUE ) archive data and new low-resolution optical data for the T Tauri star LkH α 264 covering the region from 1200 to 7000 Å. The UV continuum is well fitted by the combination of a blackbody at 4300 K plus hydrogenic free–free and free–bound emission from a dense plasma at 3.5×10⁴ K plus the emission by a second blackbody. This last component is at T ≈8700 K and covers about 4 per cent of the stellar surface. We interpret this last component to be the result of emission from one or various hotspots. The interesting result is that this combined emission also fits the observed optical continuum well. We conclude that this star is an analogue of the Sun, however displaying a much higher level of activity.     

The enigma of the oldest 'nova': the central star and nebula of CK Vul

CK Vul is classified as, amongst others, the slowest known nova, a hibernating nova or a very late thermal pulse object. Following its eruption in ad 1670, the star remained visible for 2 yr. A 15-arcsec nebula was discovered in the 1980s, but the star itself has not been detected since the eruption. We here present radio images which reveal a 0.1-arcsec radio source with a flux of 1.5 mJy at 5 GHz. Deep Hα images show a bipolar nebula with a longest extension of 70 arcsec, with the previously known compact nebula at its waist. The emission-line ratios show that the gas is shock-ionized, at velocities  >100 km s⁻¹  . Dust emission yields an envelope mass of  ∼5 × 10⁻² M_⊙  . Echelle spectra indicate outflow velocities up to 360 km s⁻¹. From a comparison of images obtained in 1991 and 2004 we find evidence for expansion of the nebula, consistent with an origin in the 1670 explosion; the measured expansion is centred on the radio source. No optical or infrared counterpart is found at the position of the radio source. The radio emission is interpreted as thermal free–free emission from gas with   T _e∼ 10⁴ K  . The radio source may be due to a remnant circumbinary disc, similar to those seen in some binary post-AGB stars. We discuss possible classifications of this unique outburst, including that of a sub-Chandrasekhar mass supernova, a nova eruption on a cool, low-mass white dwarf or a thermal pulse induced by accretion from a circumbinary disc.     

IPHAS discoveries of young stars towards Cyg OB2 and its southern periphery

We report on the discovery of over 50 strong Hα emitting objects towards the large OB association Cyg OB2 and the H  ii region DR 15 on its southern periphery. This was achieved using the INT Photometric Hα Survey of the Northern Galactic Plane (IPHAS), combined with follow-up spectroscopy using the MMT multi-object spectrometer HectoSpec. We present optical spectra, supplemented with optical r ',  i ' and H α photometry from IPHAS, and near-infrared J ,  H and K photometry from Two Micron All Sky Survey. The position of the objects in the ( J − H ) versus ( H − K ) diagram strongly suggests most of them are young. Many show Ca  ii infrared triplet emission indicating that they are in a pre-main-sequence phase of evolution of T Tauri and Herbig Ae nature. Among these, we have uncovered pronounced clustering of T Tauri stars roughly a degree south of the centre of Cyg OB2, in an arc close to the H  ii region DR 15, and the radio ring nebula G79.29+0.46, for which we discuss its candidacy as a luminous blue variable. The emission-line objects towards Cyg OB2 itself could be the brightest most prominent component of a population of lower mass pre-main-sequence stars that has yet to be uncovered. Finally, we discuss the nature of the ongoing star formation in Cyg OB2 and the possibility that the central OB stars have triggered star formation in the periphery.     

The emergence of a neutral Herbig–Haro jet into a photoionized nebula

Recent observations show the existence of an increasing number of collimated outflows ejected by young, low-mass stars which are embedded in H  ii regions. At distances of a few tens of au from the star, at least one lobe of these outflows will be shielded from the ambient ionizing radiation by the compact, high-extinction circumstellar disc. Within these shielded regions, the jets are probably mostly neutral, similar to the jets in 'normal' Herbig–Haro (HH) objects. At larger distances, these jets emerge into the photoionized nebula, and start to be photoionized by the radiation from the ionizing photon source of the nebula.
In this paper, we model the photoionization of an initially neutral HH jet. This process begins as an ionization front at the side of the jet, which is directed towards the ionizing star of the nebula, and progresses into the beam of the jet. There are two possible solutions. In the first solution, the jet beam becomes fully ionized through the passage of an R-type ionization front. In the second solution, the ionization front slows down enough to become a D-type front (or is already a D-type front at the point in which the jet emerges into the photoionized nebula), forming a partially ionized jet beam, with an expanding photoionized region and a compressed neutral region.
We explore these two types of solutions both analytically and numerically, and discuss the observational effects introduced by this jet photoionization process, concentrating in a region of parameter space that straddles the parameters deduced for HH 444 (the jet from V 510 Orionis).     

Near-infrared and optical emission-line structure of the Keyhole Nebula in NGC 3372

Narrow-band infrared and optical images of the Keyhole Nebula in NGC 3372 reveal which structures are caused by extinction, and show the underlying morphology of photoionized and shock-excited gas. Dark clouds conspire with ionized gas to create the apparent keyhole shape, which is prominent at blue wavelengths and less apparent in the infrared. The  Pa β /H α   line ratio shows the spatial distribution of foreground extinction. The wavelength dependence of this extinction indicates a reddening law with   R ≈4.8  , different from the normal interstellar medium. This confirms previous estimates of reddening toward the Carina Nebula determined from stellar photometry, and reveals that the anomalous extinction is patchy and within the H  ii region. The morphology of the ionized gas is different from the extinction clouds; it shows an edge-on ionization front running NE to SW, with a limb-brightened indentation that forms the upper outline of the keyhole shape. A fast polar wind from η Carinae may have punctured the ionization front, since the indentation is directly along a projection of the polar axis of the star. This is supported by the morphology of shock-excited gas revealed by a high  [S  ii ]/H α   ratio. High-excitation gas emitting [O  iii ] and He  i has a smoother distribution. Molecular clumps in the region are also discussed.     

Non-emission-line young stars of intermediate mass

We present optical spectra of four intermediate-mass candidate young stellar objects that have often been classified as Herbig Ae/Be stars. Typical Herbig Ae/Be emission features are not present in the spectra of these stars. Three of them, HD 36917, HD 36982 and HD 37062, are members of the young Orion nebula cluster (ONC). This association constrains their ages to be ≲1 Myr. The lack of appreciable near-infrared excess in them suggests the absence of hot dust close to the central star. However, they do possess significant amounts of cold and extended dust as revealed by the large excess emission observed at far-infrared wavelengths. The fractional infrared luminosities  ( L _ir/ L _★)  and the dust masses computed from IRAS fluxes are systematically lower than those found for Herbig Ae/Be stars but higher than those for Vega-like stars. These stars may thus represent the youngest examples of the Vega phenomenon known so far. In contrast, the other star in our sample, HD 58647, is more likely to be a classical Be star, as is evident from the low   L _ir/ L _★  , the scarcity of circumstellar dust, the low polarization, the presence of H α emission and near-infrared excess, and the far-infrared spectral energy distribution consistent with free–free emission similar to other well-known classical Be stars.     

Circumstellar structure of RU Lupi down to au scales

We have used the technique of spectro-astrometry to study the milliarcsecond scale structure of the emission lines in the T Tauri star RU Lupi. The wings of the H α emission are found to be displaced from the star towards the south-west (blue wing) and north-east (red wing) with angular scales of 20–30 mas. This structure is consistent with a bipolar outflow from the star. From a study of the variability of the intensity and position spectra, we argue that a combination of magnetically driven bipolar outflow and accreting gas contributes to the H α emission. On the other hand, the [O  i ] and [S  ii ] emission are displaced from the star to the south-west but at much larger distances than the H α , hundreds of milliarcseconds for the high-velocity component (HVC) and down to 30 mas for the low-velocity components (LVCs). The presence of both redshifted and blueshifted outflows in H α but only a blueshifted outflow in the forbidden lines can be explained if the disc obscures the redshifted forbidden line outflow, but a disc gap with outer radius 3–4 au allows the redshifted H α to be seen. This gap could be induced by an unseen companion.     

IRAS 17213-3841:晚型富碳星还是早型发射线星?

IRAS 17213-3841作为富碳星列于新版碳星星表中．然而该星的IRAS低分辨率光谱显示富氧的硅酸盐发射特征；光谱观测结果表明，该星是一个接近零龄主序的，光谱型为O9／B0的早型发射线星，而不是碳星，因此应从碳星星表中剔除．此外，将它证认为碳星的近红外-IRAS双色图方法并不是一个完全可靠的方法，用这一方法来证认碳星必须十分小心．     

WR 7a: a V Sagittae or a qWR star?

The star WR 7a, also known as SPH 2, has a spectrum that resembles that of V Sagittae stars although no O  vi emission has been reported. The Temporal Variance Spectrum – TVS – analysis of our data shows weak but strongly variable emission of O  vi lines which is below the noise level in the intensity spectrum.
Contrary to what is seen in V Sagittae stars, optical photometric monitoring shows very little, if any, flickering. We found evidence of periodic variability. The most likely photometric period is   P _phot= 0.227(±14) d  , while radial velocities suggest a period of   P _spec= 0.204(±13) d  . One-day aliases of these periods can not be ruled out. We call attention to similarities with HD 45166 and DI Cru (= WR 46), where multiple periods are present. They may be associated to the binary motion or to non-radial oscillations.
In contrast to a previous conclusion by Pereira et al., we show that WR 7a contains hydrogen. The spectrum of the primary star seems to be detectable as the N  v 4604 Å  absorption line is visible. If so, it means that the wind is optically thin in the continuum and that it is likely to be a helium main sequence star.
Given the similarity to HD 45166, we suggests that WR 7a may be a qWR – quasi Wolf–Rayet – star. Its classification is WN4h/CE in the Smith, Shara & Moffat three-dimensional classification system.     

Correlated optical/X-ray variability in the high-mass X-ray binary SAX J2103.5+4545

SAX J2103.5+4545 is the Be/X-ray binary (BeX) with the shortest orbital period. It shows extended bright and faint X-ray states that last for a few hundred days. The main objective of this work is to investigate the relationship between the X-ray and optical variability and to characterize the spectral and timing properties of the bright and faint states. We have found a correlation between the spectral and temporal parameters that fit the energy and power spectra. Softer energy spectra correspond to softer power spectra. That is to say, when the energy spectrum is soft, the power at high frequencies is suppressed. We also present the results of our monitoring of the Hα line of the optical counterpart since its discovery in 2003. There is a correlation between the strength and shape of the Hα line, originated in the circumstellar envelope of the massive companion and the X-ray emission from the vicinity of the neutron star. Hα emission, indicative of an equatorial disc around the B-type star, is detected whenever the source is bright in X-rays. When the disc is absent, the X-ray emission decreases significantly. The long-term variability of SAX J2103.5+4545 is characterized by fast episodes of disc loss and subsequent reformation. The time-scales for the loss and reformation of the disc (about 2 yr) are the fastest among BeXs.     

Discs and the 10-μm silicate spectra of young stellar objects with non-photospheric continua

Dust emission in the non-photospheric 10-μm continua of HL Tau and Taurus-Elias 7 (Haro6-10, GV Tau) is distinguished from foreground silicate absorption using a simple disc model with radial power-law temperature and mass–density distributions based on the IR–submm model of T Tauri stars by Adams, Lada & Shu with foreground extinction. The resulting 10-μm absorption profiles are remarkably similar to those of the field star Taurus-Elias 16 obtained by Bowey, Adamson & Whittet. The fitted temperature indices are 0.44 (HL Tau) and 0.33 (Elias 7) in agreement with Boss's theoretical models of the 200–300 K region, but lower than those of IR–submm discs (0.5–0.61; Mannings & Emerson); a significant fraction of the modelled 10-μm emission of HL Tau is optically thin, whilst that of Elias 7 is optically thick. We suggest that HL Tau's optically thin component arises from silicate dust within low-density layers above an optically thick disc.