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1.
We present mid-infrared (MIR) photometry for 367 Galactic disc, bulge and Large Magellanic Cloud (LMC) planetary nebulae (PNe), determined using data acquired with the Spitzer Space Telescope , and through the Legacy Programs GLIMPSE II (Galactic Legacy Infrared Mid-plane Survey Extraordinaire II) and SAGE (Surveying the Agents of the Galaxy's Evolution). This has permitted us to make a comparison between the luminosity functions of bulge and LMC PNe, and between the MIR colours of all three categories of source. It is determined that whilst the  3.6 μm  luminosity functions of the LMC and bulge sources are likely to be closely similar, the [3.6]–[5.8] and [5.8]–[8-0] indices of LMC nebulae are different from those of their disc and bulge counterparts. This may arise because of enhanced  6.2 μm  polycyclic aromatic hydrocarbon emission within the LMC sources, and/or as a result of further, and more radical differences between the spectra of LMC and Galactic PNe. We also determine that the more evolved disc sources listed in the Macquarie/AAO/Strasbourg (MASH) catalogues of Parker et al. and Miszalski et al. have similar colours to those of the less evolved (and higher surface brightness) sources in the catalogue of Acker et al., a result which appears at variance with previous studies of these sources.  相似文献   

2.
We investigate the Galactic disc distribution of a sample of planetary nebulae characterized in terms of their mid-infrared spectral features. The total number of Galactic disc PNe with 8–13 μm spectra is brought up to 74 with the inclusion of 24 new objects, the spectra of which we present for the first time. 54 PNe have clearly identified warm dust emission features, and form a sample that we use to construct the distribution of the C/O chemical balance in Galactic disc PNe. The dust emission features complement the information on the progenitor masses brought by the gas-phase N/O ratios: PNe with unidentified infrared emission bands have the highest N/O ratios, while PNe with the silicate signature have either very high N enrichment or close to none. We find a trend for a decreasing proportion of O-rich PNe towards the third and fourth Galactic quadrants. Two independent distance scales confirm that the proportion of O-rich PNe decreases from     per cent inside the solar circle to     per cent outside. PNe with warm dust are also the youngest. PNe with no warm dust are uniformly distributed in C/O and N/O ratios, and do not appear to be confined to     They also have higher 6-cm fluxes, as expected from more evolved PNe. We show that the IRAS fluxes are a good representation of the bolometric flux for compact and IR-bright PNe, which are probably optically thick. Selection of objects with     should probe a good portion of the Galactic disc for these young, dense and compact nebulae, and the dominant selection effects are rooted in the PN catalogues.  相似文献   

3.
We have analysed the near-infrared (NIR) and far-infrared (FIR) colours of MASH I and MASH II (the Macquarie/AAO/Strasbourg surveys) planetary nebulae (PNe), using data deriving from the Two-Micron All-Sky Survey and Infrared Astronomical Satellite . We were able to identify ∼5 per cent of the sources in the NIR, and a slightly larger fraction (∼12 per cent) in the FIR. It is concluded that whilst the NIR colours of these nebulae are consistent with those of less evolved (and higher surface brightness) PNe, their FIR colours are markedly different. This disparity is likely to arise as a result of an evolution in dust temperatures, in their line emission characteristics, and in the relative contributions of the 8.6 and 11.3 μm polycyclic aromatic hydrocarbon emission features. A rump of ∼9 per cent of the detected sources have values  log[ F (25 μm)/ F (60 μm)]  which are lower than can be explained in terms of normal nebular evolution, however. If these are comparable in nature to the undetected PNe, then this would argue that ∼1 in 10 of MASH I and II nebulae may represent galactic H  ii regions, Stromgren spheres, symbiotic nebulae or other unrelated categories of source.  相似文献   

4.
The University of Tasmania Mt Pleasant 26-m and Ceduna 30-m radio telescopes have been used to search for 6.7-GHz class II methanol masers towards 200 GLIMPSE ( The Galactic Legacy Infrared Mid-Plane Survey Extraordinaire ) sources. The target regions were selected on the basis of their mid-infrared colours as being likely to be young high-mass star formation regions and are either bright at 8.0 μm, or have extreme [3.6]–[4.5] colour. Methanol masers were detected towards 38 sites, nine of these being new detections. The prediction was that approximately 20 new 6.7-GHz methanol masers would be detected within 3.5 arcmin of the target GLIMPSE sources, but this is the case for only six of the new detections. A number of possible reasons for the discrepancy between the predicted and actual number of new detections have been investigated. It was not possible to draw any firm conclusions as to the cause, but it may be because many of the target sources are at an evolutionary phase prior to that associated with 6.7-GHz methanol masers. Through comparison of the spectra collected as part of this search with those in the literature, the average lifetime of individual 6.7-GHz methanol maser spectral features is estimated to be around 150 yr, much longer than is observed for 22-GHz water masers.  相似文献   

5.
A sample of 25 infrared-bright planetary nebulae (PNe) towards the Galactic bulge is analysed through 8–13 μm spectroscopy. The classification of the warm dust emission features provides a measure of the C/O chemical balance, and represents the first C/O estimates for bulge PNe. Out of 13 PNe with identified dust types, four PNe have emission features associated with C-based grains, while the remaining 9 have O-rich dust signatures. The low fraction of C-rich PNe, ≲ 30 per cent, contrasts with that for local PNe, around ∼ 80 per cent, although it follows the trend for a decreasing frequency of C-rich PNe with galactocentric radius (Paper I). We investigate whether the PNe discussed here are linked to the bulge stellar population (similar to type IV, or halo, PNe) or the inner Galactic disc (a young and super-metal-rich population). Although 60 per cent of the PNe with warm dust are convincing bulge members, none of the C-rich PNe satisfies our criteria, and they are probably linked to the inner Galactic disc. In the framework of single star evolution, the available information on bulge PNe points towards a progenitor population similar in age to that of local PNe (type I PNe are found in similar proportions), but super-metal-rich (to account for the scarcity of C-rich objects). Yet the metallicities of bulge PNe, as inferred from [O/H], fail to reach the required values – except for the C-rich objects. It is likely that the sample discussed here is derived from a mixed disc/bulge progenitor population and dominated by type IV PNe, as suggested by Peimbert. The much higher fraction of O-rich PNe in this sample than in the solar neighbourhood should result in a proportionally greater injection of silicate grains into the inner Galactic medium.  相似文献   

6.
High-resolution far-infrared observations of a large area of the star-forming complex RCW 106 obtained using the TIFR 1-m balloon-borne telescope are presented. Intensity maps have been obtained simultaneously in two bands centred around 150 and 210 μm. Intensity maps have also been obtained in the four IRAS bands using HIRES-processed IRAS data. From the 150- and 210-μm maps, reliable maps of dust temperature and optical depth have been generated. The star formation in this complex has occurred in five linear sub-clumps. Using the map at 210 μm, which has a spatial resolution superior to that of IRAS at 100 μm, 23 sources have been identified. The spectral energy distribution (SED) and luminosity of these sources have been determined using the associations with the IRAS maps. The luminosity distribution of these sources has been obtained. Assuming these embedded sources to be zero-age main-sequence stars and using the mass–luminosity relation for these, the power-law slope of the initial mass function is found to be −1.73±0.5 . This index for this very young complex is about the same as that for more evolved complexes and clusters. Radiation transfer calculations in spherically symmetric geometry have been undertaken to fit the SEDs of 13 sources with fluxes in both the TIFR and the IRAS bands. From this, the r −2 density distribution in the envelopes is ruled out. Finally, a correlation is seen between the luminosity of embedded sources and the computed dust masses of the envelopes.  相似文献   

7.
Certain hydrodynamic models of planetary nebulae (PNe) suggest that their shells possess appreciable radial density gradients. However, the observational evidence for such gradients is far from clear. On the one hand, Taylor et al. claim to find evidence for radio spectral indices  0.6 < α < 1.8  , a trend which is taken to imply a variation   n e∝ r −2  in most of their sample of PNe. On the other hand, Siódmiak & Tylenda find no evidence for any such variations in density; shell inhomogeneities, where they occur, are primarily attributable to 'blobs or condensations'.
It will be suggested that both of these analyses are unreliable, and should be treated with a considerable degree of caution. A new analysis within the  log( F (5 GHz)/ F (1.4 GHz))–log( T B(5 GHz))  plane will be used to show that at least 10–20 per cent of PNe are associated with strong density gradients. We shall also show that the ratio   F (5 GHz)/ F (1.4 GHz)  varies with nebular radius; an evolution that can be interpreted in terms of varying shell masses, and declining electron densities.  相似文献   

8.
We report the extragalactic radio-continuum detection of 15 planetary nebulae (PNe) in the Magellanic Clouds (MCs) from recent Australia Telescope Compact Array+Parkes mosaic surveys. These detections were supplemented by new and high-resolution radio, optical and infrared observations which helped to resolve the true nature of the objects. Four of the PNe are located in the Small Magellanic Cloud (SMC) and 11 are located in the Large Magellanic Cloud (LMC). Based on Galactic PNe the expected radio flux densities at the distance of the LMC/SMC are up to ∼2.5 and ∼2.0 mJy at 1.4 GHz, respectively. We find that one of our new radio PNe in the SMC has a flux density of 5.1 mJy at 1.4 GHz, several times higher than expected. We suggest that the most luminous radio PN in the SMC (N S68) may represent the upper limit to radio-peak luminosity because it is approximately three times more luminous than NGC 7027, the most luminous known Galactic PN. We note that the optical diameters of these 15 Magellanic Clouds (MCs) PNe vary from very small (∼0.08 pc or 0.32 arcsec; SMP L47) to very large (∼1 pc or 4 arcsec; SMP L83). Their flux densities peak at different frequencies, suggesting that they may be in different stages of evolution. We briefly discuss mechanisms that may explain their unusually high radio-continuum flux densities. We argue that these detections may help solve the 'missing mass problem' in PNe whose central stars were originally  1–8 M⊙  . We explore the possible link between ionized haloes ejected by the central stars in their late evolution and extended radio emission. Because of their higher than expected flux densities, we tentatively call this PNe (sub)sample –'Super PNe'.  相似文献   

9.
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.  相似文献   

10.
The UV-Excess survey of the northern Galactic plane images a  10°× 185°  wide band, centred on the Galactic equator using the 2.5-m Isaac Newton Telescope in four bands (       i  5875) down to  ∼21–22  mag (     in       i  5875). The setup and data reduction procedures are described. Simulations of the colours of main-sequence stars, giant, supergiants, DA and DB white dwarfs and AM Canum Venaticorum stars are made, including the effects of reddening. A first look at the data of the survey (currently 30 per cent complete) is given.  相似文献   

11.
We present a careful analysis of the point-source detection limit of the AKARI All-Sky Survey in the WIDE-S 90-μm band near the North Ecliptic Pole (NEP). Timeline analysis is used to detect IRAS ( Infrared Astronomy Satellite ) sources and then a conversion factor is derived to transform the peak timeline signal to the interpolated 90-μm flux of a source. Combined with a robust noise measurement, the point-source flux detection limit at signal-to-noise ratio  (S/N) > 5  for a single detector row is  1.1 ± 0.1 Jy  which corresponds to a point-source detection limit of the survey of ∼0.4 Jy.
Wavelet transform offers a multiscale representation of the Time Series Data ( tsd ). We calculate the continuous wavelet transform of the tsd and then search for significant wavelet coefficients considered as potential source detections. To discriminate real sources from spurious or moving objects, only sources with confirmation are selected. In our multiscale analysis, IRAS sources selected above 4σ can be identified as the only real sources at the Point Source Scales. We also investigate the correlation between the non- IRAS sources detected in timeline analysis and cirrus emission using wavelet transform and contour plots of wavelet power spectrum. It is shown that the non- IRAS sources are most likely to be caused by excessive noise over a large range of spatial scales rather than real extended structures such as cirrus clouds.  相似文献   

12.
We present photometric analysis of deep mid-infrared (mid-IR) observations obtained by Spitzer /IRAC covering the fields Q1422+2309, Q2233+1341, DSF2237a,b, HDFN, SSA22a,b and B20902+34, giving the number counts and the depths for each field. In a sample of 751 Lyman-break galaxies (LBGs) lying in those fields, 443, 448, 137 and 152 are identified at 3.6-, 4.5-, 5.8-, 8.0-μm IRAC bands, respectively, expanding their spectral energy distribution to rest-near-IR and revealing that LBGs display a variety of colours. Their rest-near-IR properties are rather inhomogeneous, ranging from those that are bright in IRAC bands and exhibit  [ R ]−[3.6] > 1.5  colours to those that are faint or not detected at all in IRAC bands with  [ R ]−[3.6] < 1.5  colours and these two groups of LBGs are investigated. We compare the mid-IR colours of the LBGs with the colours of star-forming galaxies and we find that LBGs have colours consistent with star-forming galaxies at   z ∼ 3  . The properties of the LBGs detected in the 8-μm IRAC band (rest-frame K band) are examined separately, showing that they exhibit redder  [ R ]−[3.6]  colours than the rest of the population and that although in general, a multiwavelength study is needed to reach more secure results, IRAC 8-μm band can be used as a diagnostic tool, to separate high z , luminous AGN-dominated objects from normal star-forming galaxies at   z ∼ 3  .  相似文献   

13.
Near-infrared photometry was performed on 56 southern 6.7-GHz methanol maser sources. A simple spherically symmetric model of the radiative transfer through a dust shell was developed and used to study the conditions in the dust cloud in which the masers are produced. The parameters investigated were the size of the cloud, the spectral type of the embedded star, the optical depth of the dust cloud and the dust density distribution. It was found that the infrared colours of the models have a complex dependence on the parameters and that no unique combination of parameter values explains the spectral energy distribution of any particular source. The model effectively reproduces the far-infrared ( IRAS ) colours but cannot simultaneously explain the near-infrared colours for any of the observed sources.  相似文献   

14.
We have carried out a spectroscopic survey of 750 sources that are strong 25-μm emitters from the IRAS Faint Source data base. Many of these sources are previously unknown active galactic nuclei including new IRAS quasars, three of which we describe here: F21382−2659, Z06367−6845 and Z05558−5008. They are all radio and X-ray quiet, and compared to the known IRAS quasars they have similar 25-μm luminosities, L (25 μm), but lower values of L (25 μm)/ L ( B ). Their F (25 μm)/ F (60 μm) IRAS colours lie in the range 0.33 to 1.08, indicating the presence of relatively warm dust, presumably in a dusty torus surrounding the central source, and with temperatures similar to those of the known IRAS quasars. The quasar with the warmest dust, F21382−2659, exhibits broad (full width at half-maximum ∼4000 km s−1) asymmetric Balmer lines with H γ having an opposite asymmetry to the other broad lines; also H β (only) is double-peaked. Fe  ii is very weak in F21382−2659 but strong in the other two quasars, and the anticorrelation between Fe  ii and [O  iii ] holds as anticipated. Two of the quasars are unpolarized: although F21382−2659 is optically polarized (2.1 per cent at 4950 Å), we argue that this provides little insight into the orientation of its dust torus relative to the line of sight.  相似文献   

15.
For this paper, we collected almost all of the type II quasars so far discovered. Among them, 485 sources have photometric data at JHK bands, mainly from Two-Micron All-Sky Survey observations, 65 sources have IRAS photometric data in at least one of the three IRAS bands at 25, 60 and 100 μm and 15 sources have IRAS photometric data in all three IRAS bands. We find that in nearly half of all type II quasars, both the near- and far-infrared radiations are dominated by starlight or thermal reprocessing of starlight by dust in the underlying galaxy. The infrared radiation of the other group (slightly over half) is dominated by a non-thermal radiation in the near-infrared, and mostly in the far-infrared also (although there is a mixture particularly for the longer wavelengths). It is proposed that for the later group, hidden broad lines may exist in the infrared. On the basis of our and previous results, we also discuss the possibility that there are two distinct classes of type II quasars: 'true' type II quasars without a broad-line region and heavily obscured type I quasars, in full analogy with the case for type II Seyfert galaxies. No relationships can be found for either the near-infrared or the far-infrared colours and the redshift. Correlations between absolute magnitude in the near- and far-infrared with redshift are found, but could be due to a flux limit (Malmquist bias).  相似文献   

16.
We calculate the X-ray emission from the shocked fast wind blown by the central stars of planetary nebulae (PNe) and compare with observations. Using spherically symmetric self-similar solutions, we calculate the flow structure and X-ray temperature for a fast wind slamming into a previously ejected slow wind. We find that the observed X-ray emission of six PNe can be accounted for by shocked wind segments that were expelled during the early-PN phase, if the fast wind speed is moderate,   v 2∼ 400–600 km s−1  , and the mass-loss rate is a few times  10−7 M⊙ yr−1  . We find, as proposed previously, that the morphology of the X-ray emission is in the form of a narrow ring inner to the optical bright part of the nebula. The bipolar X-ray morphology of several observed PNe, which indicates an important role of jets, rather than a spherical fast wind, cannot be explained by the flow studied here.  相似文献   

17.
We report the discovery of H2 line emission associated with 6.67-GHz methanol maser emission in massive star-forming regions. In our UNSWIRF/AAT observations, H2 1–0 S(1) line emission was found associated with an ultracompact H  ii region IRAS 14567–5846 and isolated methanol maser sites in G318.95–0.20 , IRAS 15278–5620 and IRAS 16076–5134 . Owing to the lack of radio continuum in the latter three sources, we argue that their H2 emission is shock excited, while it is UV-fluorescently excited in IRAS 14567–5846 . Within the positional uncertainties of 3 arcsec, the maser sites correspond to the location of infrared sources. We suggest that 6.67-GHz methanol maser emission is associated with hot molecular cores, and propose an evolutionary sequence of events for the process of massive star formation.  相似文献   

18.
The central stars of highly evolved planetary nebulae (PNe) are expected to have closely similar absolute visual magnitudes MV . This enables us to determine approximate distances to these sources where one knows their central star visual magnitudes, and levels of extinction. We find that such an analysis implies values of D which are similar to those determined by Phillips; Cahn, Kaler & Stanghellin; Acker, and Daub. However, our distances are very much smaller than those of Zhang; Bensby & Lundstrom, and van de Steene & Zijlstra. The reasons for these differences are discussed, and can be traced to errors in the assumed relation between brightness temperature and radius.
Finally, we determine that the binary companions of such stars can be no brighter than   MV ∼ 6 mag  , implying a spectral type of K0 or later in the case of main-sequence stars.  相似文献   

19.
We present the Macquarie/AAO/Strasbourg Hα Planetary Nebula Catalogue (MASH) of over 900 true, likely and possible new Galactic planetary nebulae (PNe) discovered from the AAO/UKST Hα survey of the southern Galactic plane. The combination of depth, resolution, uniformity and areal coverage of the Hα survey has opened up a hitherto unexplored region of parameter space permitting the detection of this significant new PN sample. Away from the Galactic bulge the new PNe are typically more evolved, of larger angular extent, of lower surface brightness and more obscured (i.e. extinguished) than those in most previous surveys. We have also doubled the number of PNe in the Galactic bulge itself and although most are compact, we have also found more evolved examples. The MASH catalogue represents the culmination of a seven-year programme of identification and confirmatory spectroscopy. A key strength is that the entire sample has been derived from the same, uniform observational data. The 60 per cent increase in known Galactic PNe represents the largest ever incremental sample of such discoveries and will have a significant impact on many aspects of PN research. This is especially important for studies at the faint end of the PN luminosity function which was previously poorly represented.  相似文献   

20.
We explore the nature of X-ray sources with  70 μm  counterparts selected in the Spitzer Wide-Area Infrared Extragalactic Survey (SWIRE) fields: ELAIS-N1, Lockman Hole and Chandra Deep Field South, for which Chandra X-ray data are available. A total of 28 X-ray/  70 μm  sources in the redshift interval  0.5 < z < 1.3  are selected. The X-ray luminosities and the shape of the X-ray spectra show that these sources are active galactic nuclei (AGN). Modelling of the optical to far-infrared (IR) spectral energy distribution indicates that most of them (27/28) have a strong starburst component  (>50 M⊙ yr−1)  that dominates in the IR. It is found that the X-ray and IR luminosities of the sample sources are broadly correlated, consistent with a link between AGN activity and star formation. Contrary to the predictions of some models for the co-evolution of AGN and galaxies, the X-ray/  70 μm  sources in the sample are not more obscured at X-ray wavelengths compared to the overall X-ray population. It is also found that the X-ray/  70 μm  sources have lower specific star formation rates compared to the general  70 μm  population, consistent with AGN feedback moderating the star formation in the host galaxies.  相似文献   

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