Search

Galactic supernova remnants (SNRs) with angular dimensions greater than a few degrees are relatively rare, as are remnants located more than ten degrees off the Galactic plane. Here we report a UV and optical investigation of two previously suspected SNRs more than ten degrees in both angular diameter and Galactic latitude. One is a proposed remnant discovered in 2008 through 1420 MHz polarization maps near Galactic coordinates $l$ = 353, $b$ = $-$34. GALEX far UV (FUV) and H$\alpha$ emission mosaics show the object's radio emission coincident with a 11 x 14 degree shell of UV filaments surrounding a diffuse H$\alpha$ emission ring. Another proposed high latitude SNR is the 20 x 26 degree Antlia nebula (G275.5+18.4) discovered in 2002 through low-resolution all-sky H$\alpha$ and ROSAT soft X-ray emissions. GALEX UV and H$\alpha$ mosaics along with optical spectra indicate the presence of shocks throughout the Antlia nebula with estimated shock velocities of 70 to over 100 km s$^{-1}$. We also present evidence that it has collided with the northeast rim of the Gum Nebula. We find both of these nebulae are bona fide SNRs with ages less than 10$^{5}$ yr despite their unusually large angular dimensions. We also present FUV and optical images along with optical spectra of a new high-latitude SNR (G249.7+24.7) some 4.5 degrees in diameter which has also been independently discovered in X-rays and radio (Becker at al. 2021). We find this remnant's distance to be $\leq$400 pc based on the detection of red and blue shifted Na I absorption features in the spectra of two background stars., Comment: 32 pages, 21 figures, 4 tables; Revised to match published version in the Astrophysical Journal

The dependence of the scatter broadening of extragalactic sources on the dispersion measures of distant pulsars observed along nearby lines of sight and the dependence of broadening of pulsar pulses on the scatter broadening observed for the pulsars themselves and for extragalactic sources observed along nearby lines of sight are constructed and analyzed. These dependences can be used to study turbulent plasma in the Galaxy. The effective scattering layer in the direction toward the pulsar B1933+16 is located in the Sagittarius arm at a distance of ≈3.4 kpc from the observer, and has an extent of ≈0.55 kpc. The scatter broadening and pulse broadening of B0833-45 are due to the turbulent medium in the shell of the Gum Nebula. The distance from the pulsar to the center of the scattering layer is≈43 pc. Data on scattering of the radiation of the pulsar B1818-04 and of the extragalactic source J1821-0502, together with data on the distribution of OB stars in the direction toward this pulsar, are used to show that the distance to the pulsar is ≈0.6 kpc; an H II region around the O7V star HD 171198, located 0.42 kpc from the Sun, is responsible for the scattering of this pulsar’s radiation.

The high sensitivity and wide frequency coverage of the Murchison Widefield Array allow for the measurement of the spectral scaling of the pulsar scattering timescale, $\alpha$, from a single observation. Here we present three case studies targeted at bright, strongly scattered pulsars J0534+2200 (the Crab pulsar), J0835-4510 (the Vela pulsar) and J0742-2822. We measure the scattering spectral indices to be $-3.8\pm0.2$, $-4.0\pm1.5$, and $-2.5\pm0.6$ for the Crab, Vela, and J0742-2822, respectively. We find that the scattered profiles of both Vela and J0742-2822 are best described by a thin screen model where the Gum Nebula likely contributes most of the observed scattering delay. For the Crab pulsar we see characteristically different pulse shapes compared to higher frequencies, for which none of the scattering screen models we explore are found to be optimal. The presence of a finite inner scale to the turbulence can possibly explain some of the discrepancies., Comment: 14 pages, 8 figures, accepted for publication in ApJ

We have conducted a high-dispersion ($R \sim$ 34,000) optical spectroscopic study of 10 young stars near the cometary gloule CG 30 in the Gum Nebula, a diffuse H \textsc{ii} region home to at least 32 cometary globules. All 10 spectroscopically observed stars at the nebula's northern edge are of low mass (spectral types M4.5 - K5), have broad H$\alpha$ emission, and show spectral veiling. Eight of the 10 are classical T Tauri stars. We spectroscopically measure the photospheric properties of CG 30 IRS 4 inside CG 30. Though embedded, CG 30 IRS 4 is T Tauri-like, with relatively slow projected rotation and moderate veiling. Undepleted Li absorptions, strong H$\alpha$ emissions, and positions well above the main sequence on an HR diagram suggest the 10 stars are $\lesssim$1 Myr old. Using our measurements, previous spectroscopy, and previous photometry of 11 other young stars in the area, we determine stellar, kinematic, and accretion properties of a total of 21 young stars. Shared radial velocities, proper motions, distances, and ages suggest 14 of the young stars (including CG 30 IRS 4) are kinematically related to CG 30. From \textit{Gaia} DR2 distances to 6 of these stars, we derive a distance of $358.1\pm2.2$ pc to the cometary globule complex CG 30/31/38. The CG 30 association has an accretor fraction of $29\pm14$\%, low for quiescent clusters of similar age but consistent with other irradiated clusters. The Gum Nebula's moderate radiation environment ($G_0=6.6^{+3.2}_{-2.7}$ at CG 30) may be strong enough to shorten disk lifetimes., Comment: 20 pages, 7 figures, 9 tables

We report on the source Gaia 19ajj, identifying it as a young star associated with a little-studied star-forming region seen along a complex line-of-sight through the Gum Nebula. The optical lightcurve recently recorded by Gaia exhibits a slow and unsteady 5.5 mag rise over about 3 years, while the mid-infrared lightcurve from NEOWISE over the same time period shows a 1.2 mag rise having similar structure. Available color information is inconsistent with pure extinction reduction as the cause for the photometric brightening. Optical spectroscopic characteristics in the current bright phase include: little in the way of absorption except for the hallmark Li I 6707 A signature of youth plus weak e.g. Ca I and notably Ba II; strong wind/outflow in Ca II, Mg I b, Na I D, Halpha, K I, O I; jet signatures in [O I], [S II], [Ca II], [Fe II], and [Ni II]; and narrow rest-velocity emission in neutral species such as Fe I, Ni I, and Mg I. The infrared spectrum is also characterized by outflow and emission, including: a hot He I wind, jet lines such as [Fe II] and H2; and weak narrow rest-velocity atomic line emission. The 12CO bandheads are weakly in emission, but there is also broad H2O absorption. Gaia 19ajj exhibited a previous bright state in the 2010-2012 time frame. The body of photometric and spectroscopic evidence suggests that the source bears resemblance to V2492 Cyg (PTF 10nvg) and PV Cep, both of which similarly experience bright phases that recur on long timescales, with large-amplitude photometric variations and emission-dominated spectra. We interpret the behavior of Gaia 19ajj as caused by cycles of enhanced disk accretion accompanied by reduced extinction., Comment: To appear in the Astronomical Journal

We report on $UBVI$ photometry and spectroscopy for MK classification purposes carried out in the fields of five open clusters projected against the Vela Gum in the Third Galactic Quadrant of the Galaxy. They are Ruprecht 20, Ruprecht 47, Ruprecht 60, NGC 2660 and NGC 2910. We could improve/confirm the parameters of these objects derived before. The spectroscopic parallax method has been applied to several stars located in the fields of four out of the five clusters to get their distances and reddenings. With this method we found two blue stars in the field of NGC 2910 at distances that make them likely members of Vela OB1 too. Also, projected against the fields of Ruprecht 20 and Ruprecht 47 we have detected other young stars favoring not only the existence of Puppis OB1 and OB2 but conforming a young stellar group at $\sim1$ kpc from the Sun and extending for more than 6 kpc outward the Galaxy. If this is the case, there is a thickening of the thin Galactic disk of more than 300 pc at just 2-3 kpc from the Sun. Ruprecht 60 and NGC 2660 are too old objects that have no physical relation with the associations under discussion. An astonishing result has been the detection in the background of Ruprecht 47 of a young star at the impressive distance of 9.5 kpc from the Sun that could be a member of the innermost part of the Outer Arm. Another far young star in the field of NGC 2660, at near 6.0 kpc, may become a probable member of the Perseus Arm or of the inner part of the Local Arm. The distribution of young clusters and stars onto the Third Galactic Quadrant agrees with recent findings concerning the extension of the Local Arm as revealed by parallaxes of regions of star formation. We show evidences too that added to previous ones found by our group explain the thickening of the thin disk as a combination of flare and warp., Accepted for publication in New Astronomy

The Gum Nebula is 36 degree wide shell-like emission nebula at a distance of only 450 pc. It has been hypothesised to be an old supernova remnant, fossil HII region, wind-blown bubble, or combination of multiple objects. Here we investigate the magneto-ionic properties of the nebula using data from recent surveys: radio-continuum data from the NRAO VLA and S-band Parkes All Sky Surveys, and H-alpha data from the Southern H-Alpha Sky Survey Atlas. We model the upper part of the nebula as a spherical shell of ionised gas expanding into the ambient medium. We perform a maximum-likelihood Markov chain Monte-Carlo fit to the NVSS rotation measure data, using the H-halpha data to constrain average electron density in the shell $n_e$. Assuming a latitudinal background gradient in RM we find $n_e=1.3^{+0.4}_{-0.4} {\rm cm}^{-3}$, angular radius $\phi_{\rm outer}=22.7^{+0.1}_{-0.1} {\rm deg}$, shell thickness $dr=18.5^{+1.5}_{-1.4} {\rm pc}$, ambient magnetic field strength $B_0=3.9^{+4.9}_{-2.2} \mu{\rm G}$ and warm gas filling factor $f=0.3^{+0.3}_{-0.1}$. We constrain the local, small-scale (~260 pc) pitch-angle of the ordered Galactic magnetic field to $+7^{\circ}\lesssim\wp\lesssim+44^{\circ}$, which represents a significant deviation from the median field orientation on kiloparsec scales (~-7.2$^{\circ}$). The moderate compression factor $X=6.0\,^{+5.1}_{-2.5}$ at the edge of the H-alpha shell implies that the 'old supernova remnant' origin is unlikely. Our results support a model of the nebula as a HII region around a wind-blown bubble. Analysis of depolarisation in 2.3 GHz S-PASS data is consistent with this hypothesis and our best-fitting values agree well with previous studies of interstellar bubbles., Comment: 33 pages, 16 figures. Accepted by The Astrophysical Journal

We have obtained linear polarization measurements of stars along the western side of the IRAS Vela Shell toward HD 62542. From 16 CCD fields distributed along the ionization front (I-front) we have built a catalog of 856 objects with polarization signal-to-noise ratio larger than 10. We detect very significant levels of polarization and hence an appreciable magnetic field throughout the region. Composite polarization maps around the I-front are shown. In some regions the polarization vectors are parallel to the I-front, but a perpendicular trend is also evident along parts of the front. In addition, the polarization pattern seems to be affected by gas streaming inside the cloud.

To investigate the kinematics of the neutral material around the Gum nebula, emission from hydroxyl at 1667 MHz was observed at many positions over the region. Fitting models of expanding shells to these data together with previously published molecular line data shows that the diffuse molecular clouds and cometary globules form a single expanding shell centred on G261−2.5. The mean angular radius is 10.5° and its maximum radius is 14°. The models show that the distance range to the expansion centre is from 200 pc to 500 pc. The path of the runaway O-star ζ Puppis passed within

We show that (1) the newly discovered supernova remnant (SNR), GRO J0852--4642/RX J0852.0--4622, was created by a core-collapse supernova of a massive star, and (2) the same supernova event which produced the $^{44}$Ti detected by COMPTEL from this source is probably also responsible for a large fraction of the observed $^{26}$Al emission in the Vela region detected by the same instrument. The first conclusion is based on the fact that the remnant is currently expanding too slowly given its young age for it to be caused by a Type Ia supernova. If the current SNR shell expansion speed is greater than 3000 km/s, a $15 M_\odot$ Type II supernova with a moderate kinetic energy exploding at about 150 pc away is favored. If the SNR expansion speed is lower than 2000 km s$^{-1}$, as derived naively from the X-ray data, a much more energetic supernova is required to have occurred at $\sim250$ pc away in a dense environment at the edge of the Gum nebula. This progenitor has a preferred ejecta mass of $\le10 M_\odot$ and therefore, it is probably a Type Ib or Type Ic supernova. However, the required high ambient density of $n_H \ge 100 cm^{-3}$ in this scenario is difficult to reconcile with the regional CO data. A combination of our estimates of the age/energetics of the new SNR and the almost perfect positional coincidence of the new SNR with the centroid of the COMPTEL $ ^{26}$Al emission feature of the Vela region strongly favors a causal connection. If confirmed, this will be the first case where both $^{44}$Ti and $^{26}$Al are detected from the same young SNR and together they can be used to select preferred theoretical core-collapse supernova models.

We present a survey of molecular gas in the J = 1 -> 0 transition of 12CO towards the IRAS Vela shell. The shell, previously identified from IRAS maps, is a ring-like structure seen in the region of the Gum Nebula. We confirm the presence of molecular gas associated with some of the infrared point sources seen along the Shell. We have studied the morphology and kinematics of the gas and conclude that the shell is expanding at the rate of ~ 13 km/s from a common center. We go on to include in this study the Southern Dark Clouds seen in the region. The distribution and motion of these objects firmly identify them as being part of the shell of molecular gas. Estimates of the mass of gas involved in this expansion reveal that the shell is a massive object comparable to a GMC. From the expansion and various other signatures like the presence of bright-rimmed clouds with head-tail morphology, clumpy distribution of the gas etc., we conjecture that the molecular gas we have detected is the remnant of a GMC in the process of being disrupted and swept outwards through the influence of a central OB association, itself born of the parent cloud., 21 pages, 9 figures. Figure 1 is a separate jpeg file. To appear in Journal of Astrophysics and Astronomy

We report on multi-epoch, multifrequency observations of 64 pulsars with high spectral and time resolution. Scintillation parameters were obtained for 49 pulsars, including 13 millisecond pulsars. Scintillation speeds were derived for all 49, which doubles the number of pulsars with speeds measured in this way. There is excellent agreement between the scintillation speed and proper motion for the millisecond pulsars in our sample using the simple assumption of a mid-placed scattering screen. This indicates that the scaleheight of scattering electrons is similar to that of the dispersing electrons. In addition, we present observations of the Vela pulsar at 14 and 23 GHz, and show that the scintillation bandwidth scales as ν3.93 over a factor of 100 in observing frequency. We show that for PSR J0742−2822, and perhaps PSR J0837−4135, the Gum nebula is responsible for the high level of turbulence along their lines of sight, contrary to previous indications. There is a significant correlation between the scintillation speeds and the product of the pulsar's period and period derivative for the ‘normal’ pulsars. However, we believe this to be caused by selection effects both in pulsar detection experiments and in the choice of pulsars used in scintillation studies.

We present here a method to study the distribution of electron density fluctuations in pulsar directions as well as to estimate pulsar distances. The method, based on a simple two-component model of the scattering medium discussed by Gwinn et al. (1993), uses scintillation & proper motion data in addition to the measurements of angular broadening & temporal broadening to solve for the model parameters, namely, the fractional distance to a discrete scatterer and the ascociated relative scattering strength. We show how this method can be used to estimate pulsar distances reliably, when the location of a discrete scatterer (e.g. an HII region), if any, is known. Considering the specific example of PSR B0736-40, we illustrate how a simple characterization of the Gum nebula region (using the data on the Vela pulsar) is possible and can be used along with the temporal broadening measurements to estimate pulsar distances., To be published in MNRAS, 7 pages, 3 figures

Based on HI maps covering the 3 600 square degrees area delimited by , we investigated the neutral hydrogen distribution in the Gum nebula and its environments. The main result is the appearence of a huge disk of neutral gas at a kinematical distance compatible with that of the nebula, and whose angular dimensions coincide with the optical image of the Gum nebula. The disk, roughly centered at , is located at and has a radius of . We propose that this HI disk is the neutral gas component of the optical nebula, hence becoming the first time in which a structure with the dimensions of the optical nebula is detected in other wavelengths. We analyze the fitting of observations with different theoretical models and conclude that the most plausible interpretation is that the Gum nebula is a supershell produced by the action of repeated SN explosions, where the explosions may have originated in the aged association Vela OB2. In this context, the thick HI shell shown by Dubner et al.(1992) near and the Vela SNR are the debris of two of the several outbursts which started in the region about years ago. The southern boundary is distorted due to the presence of a radius shell, which appears to be an interstellar bubble driven by the stellar winds of the O–type star HD 49798.

The Local Bubble (LB), a volume of roughly 100 pc radius filled with ionized gas of high temperature and low density, is not a unique object. It is obviously surrounded by several interstellar bubbles of similar properties. Some of them are as close as to undergo interaction with the LB. Our most prominent neighbour is the Loop I superbubble formed by the Sco-Cen OB association. It is shown that this huge shell is in collision with our Local Bubble. The product of this interaction is an annular cloud of dense neutral gas at the boundary between the two bubbles. Other examples for close neighbouring bubbles are the Gum nebula, the Eridanus bubble and possibly the two radio loops II and III.

Sensitive, polarimetric observations are presented for the region of the Galactic plane 276°≥l≥238°, with a latitude coverage of +5°≥b≥-8° over most of this range. These observations were made using the Parkes 64-m radio telescope, at a frequency of 2.4 GHz. Both total-power and polarized emission are detected from the Vela supernova remnant, over an area exceeding 8° in diameter. Additionally, a number of features are identified beyond the shell of Vela, which correspond with what appear to be ejecta accelerated by the supernova explosion. Radio emission containing a significant polarized component is detected from the Gum nebula. To account for our observations, both a thermal and a non-thermal component of this emission are therefore required. The discrete SNR G 240.9-0.9 is reinterpreted as a section of this emission from the Gum nebula.

Cometary globule (CG) 1 and CG 2 are "classic" CGs in the Gum Nebula. They have compact heads and long dusty tails that point away from the centre of the Gum Nebula. We study the structure of CG 1 and CG 2 and the star formation in them to find clues to the CG formation mechanism. The two possible mechanisms, radiation-driven implosion (RDI) and a supernova (SN) blast wave, produce a characteristic mass distribution where the major part of the mass is situated in either the head (RDI) or the tail (SN). CG 1 and CG 2 were imaged in the near infrared (NIR) JsHKs bands. NIR photometry was used to locate NIR excess objects and to create extinction maps of the CGs. The A_V maps allow us to analyse the large-scale structure of CG 1 and CG 2. Archival images from the WISE and Spitzer satellites and HIRES-processed IRAS images were used to study the small-scale structure. In addition to the previously known CG 1 IRS 1 we discovered three new NIR-excess objects, two in CG 1 and one in CG 2. CG 2 IRS 1 is the first detection of star formation in CG 2. Spectral energy distribution (SED) fitting suggests the NIR-excess objects are young low-mass stars. CG 1 IRS 1 is probably a class I protostar in the head of CG 1. CG 1 IRS 1 drives a bipolar outflow, which is very weak in CO, but the cavity walls are seen in reflected light in our NIR and in the Spitzer 3.6 and 4.5 mum images. Strong emission from excited polycyclic aromatic hydrocarbon particles and very small grains were detected in the CG 1 tail. The total mass of CG 1 in the observed area is 41.9 Msun of which 16.8 Msun lies in the head. For CG 2 these values are 31.0 Msun total and 19.1 Msun in the head. The observed mass distribution does not offer a firm conclusion for the formation mechanism of these CGs: CG 1 is in too evolved a state, and in CG 2 part of the globule tail was outside the observed area. (abridged), Accepted for publication in A&A. 22 pages, 24 figures. JHKs photometry will be available electronically

We investigate the distribution of the interstellar dust towards six small volumes of the sky in the region of the Gum nebula. New high-quality four-colour uvby and H\beta\ Str\"omgren photometry obtained for 352 stars in six selected areas of Kapteyn, complemented with data obtained in a previous investigation for two of these areas, were used to estimate the colour excess and distance to these objects. The obtained colour excess versus distance diagrams, complemented with other information, when available, were analysed in order to infer the properties of the interstellar medium permeating the observed volumes. On the basis of the overall standard deviation in the photometric measurements, we estimate that colour excesses and distances are determined with an accuracy of 0.010 mag and better than 30%, respectively, for a sample of 520 stars. A comparison with 37 stars in common with the new Hipparcos catalogue attests to the high quality of the photometric distance determination. The obtained colour excess versus distance diagrams testify to the low density volume towards the observed lines-of-sight. Very few stars out to distances of 1 kpc from the Sun have colour excesses larger than E(b-y) = 0.1 mag. In spite of the low density character of the interstellar medium towards the Puppis-Vela direction, the obtained reddening as a function of the distance indicates that two or more interstellar structures are crossed towards the observed lines-of-sight. One of these structures may be associated with the very low density wall of the Local Cavity, which has a distance of 100-150 pc from the Sun. Another structure might be related to the Gum nebula, and if so, its front face would be located at about 350 pc from the Sun., Comment: Accepted by Astronomy and Astrophysics

The CG4 and Sa101 regions together cover a region of ~0.5 square degree in the vicinity of a "cometary globule" that is part of the Gum Nebula. There are seven previously identified young stars in this region; we have searched for new young stars using mid- and far-infrared data (3.6 to 70 microns) from the Spitzer Space Telescope, combined with ground-based optical data and near-infrared data from the Two-Micron All-Sky Survey (2MASS). We find infrared excesses in all 6 of the previously identified young stars in our maps, and we identify 16 more candidate young stars based on apparent infrared excesses. Most (73%) of the new young stars are Class II objects. There is a tighter grouping of young stars and young star candidates in the Sa101 region, in contrast to the CG4 region, where there are fewer young stars and young star candidates, and they are more dispersed. Few likely young objects are found in the "fingers" of the dust being disturbed by the ionization front from the heart of the Gum Nebula., Comment: Accepted for publication in AJ

We present a high resolution spectroscopic study of the ionised gas in Puppis-Vela, which includes the Gum Nebula and the IRAS Vela Shell, in the emission lines of Halpha lambda6563 angstrom, [NII] lambdalambda6548, 6584 angstrom and the [OIII] lambda5007 angstrom. Line profiles were obtained at 18 positions well distributed over the entire region. Only the [NII] line profiles in the region of the IRAS Vela Shell show double peaked profiles, consistent with an expansion velocity of 10 +/- 2km s-1. The ionised gas associated with the 36-degrees-diameter Gum Nebula does not show any such systematic motions. This is consistent with, and provides further confirmation of, the results obtained from the IRAS Super Sky Flux (ISSA) maps (Srinivasan Sahu & Blaauw 1993) that the IRAS Vela Shell and the Gum Nebula are two separate structures but seen overlapping in projection. We detected no [OIII] lambda5007angstrom emission in any of the positions observed. From the [NII]/Halpha ratio, the temperatures derived at the 18 positions vary between 5,000 to 12,0000 K.

Evidence for an enhanced rate of star formation in the cometary globules of the Gum nebula is presented. The IRAS Point Source Catalog has been searched for sources with spectral energy distributions characteristic of young stellar or protostellar objects associated with the compact heads of the cometary globules. The surface density of such sources associated with the cometary globule heads is found to be ∼3-12 times the density in dark clouds in a neighbouring comparison area and in the northern sky. The IRAS sources associated with the cometary globule heads have luminosities in the range from ∼0.5 to ∼20 L ○ ., characteristic of low-mass young stellar or protostellar objects

C18O spectral line observations, NIR spectrosopy, narrow and broad band NIR imaging and stellar J,H,Ks photometry are used to analyse the structure of the archetype cometary globule 1 (CG 1) head and the extinction of stars in its direction. A young stellar object (YSO) associated with a bright NIR nebulosity and a molecular hydrogen object (a probable obscured HH-object), were discovered in the globule. Molecular hydrogen and Br_gamma line emission is seen in the direction of the YSO. The observed maximum optical extinction in the globule head is 9.2 magnitudes. The peak N(H2) column density and the total mass derived from the extinction are 9.0 10^21 cm-2 and and 16.7 Msun (d/300pc)^2. C18O emission in the globule head is detected in a 1.5'' by 4' area with a sharp maximum SW of the YSO. Three regions can be discerned in C18O line velocity and excitation temperature. Because of variations in the C18O excitation temperature the integrated line emission does not follow the optical extinction. It is argued that the variations in the C18O excitation temperatures are caused by radiative heating by NX Pup and interaction of the YSO with the parent cloud. No indication of a strong molecular outflow from the YSO is evident in the molecular line data. The IRAS point source 07178-4429 located in the CG 1 head resolves into two sources in the HIRES enhanced IRAS images. The 12 and 25 micron emission originates mainly in the star NX Puppis and the 60 and 100 micron emission in the YSO. The IRAS FIR luminosity of the YSO is 3.1 Lsun., Language checked v2. Accepted for publication in A&A. 16 pages, 20 figures. C18O data will be available electronically

This paper is the continuation of our work of 2008 concerning the open clusters (OCs) in system of the radio loops I–IV. In the present paper we have studied the location of OCs in relation to the Local Bubble, the Eridanus Superbubble and the Gum Nebula. As before, extremely low density of OCs from Kharchenko et al. and Dias et al. catalogs in the areas of the superbubbles (SBs) is shown. At the same time, the number of OCs in the shells exceeds several times the expected number with uniform distribution within the radius of 600 pc around the Sun. Moreover, they form rather compact groups. LSR velocities of OCs are directed away from the shells and on a tangent to them. These facts can be attributed to a common process of formation of the shells and groups of OCs. The catalog age of some OCs approximately coincides with the time of passing of the bubble radius by OC and with the time of formation of elongated compact groups of OCs. Other aspects of the problem of joint studying of OCs and SBs are noted.

We report a study of the kinematics of the cometary globules in the Gum Nebula using the J = 1 yields 0 transition line of (CO-12)O. A morphological center for the system with which 60 percent of the globules are associated is identified. It is shown that the observed radial velocities of the heads of the globules are consistent with an expansion of the system. Systematic velocity gradients are present along some of the tails. The estimated expansion age and the tail stretching age are both about a few million years, suggesting a common origin for the expansion and the formation of the tails. The presence of young stars of similar ages in some of the globules points to star formation triggered by the same cause. Possible scenarios are briefly discussed.

Optical polarization maps of small nebulosities (Re5 and IRAS 08211-4158) associated with IRAS sources located in dark globules are presented and used to determine the positions of the illuminators. The IRAS 08211-4158 system is found to have two illuminators, one corresponding to the hidden IRAS source while the other is a visible star shrouded in nebulosity. These results are combined with earlier ones for CG30/HH120 and HH46/47 to look at the overall picture of low-mass star formation in the complex of dark globules within the Gum Nebula

We present the following observations of Wra 220, the H-alpha emission line star seen superposed on cometary globule 22 (CG22) on the ESO-SERC IIIaJ plates: (1) low resolution blue and red spectra (2) high resolution spectra in the region of the H-alpha 6563 angstrom line (3) near-IR photmetry (4) visual photometry from CCD images (5) IRAS Point Source Catalogue (PSC) data. Based on these data, we conclude that Wra 220 is a T-Tauri star (spectral type K2-K3) physically associated with CG22. Other properties of the star like luminosity class, spectral energy distribution, etc. have also been derived.

Hemos utilizado los datos de los relevamientos en continuo de radio en 408, 1420, 22800 y 33000 MHz, con el fin de estudiar la distribución del índice espectral en la región de la nebulosa de Gum. Después de la substracción de la emisión térmica subyacente, hemos aplicado la técnica de la Tomografía y hemos encontrado variaciones en el índice espectral de temperatura β entre el IRAS Vela Shell (IVS), una prominente estructura en forma de anillo, y la nebulosa de Gum. Estos resultados darían más apoyo a la idea de que ambas son estructuras diferentes. We have used the radio continuum survey data at 408, 1420 , 22800 and 33000 MHz in order to study the spectral index distribution in the Gum nebula region. After subtraction of the underlying thermal emission, we have applied the tomography technique and we found variations in the radio continuum temperature spectral index between the IRAS Vela shell (IVS), that is a prominent ring-like feature, and the Gum nebula. These results would provide further support to the idea that both structures are different. Fil: Testori, Juan Carlos. Provincia de Buenos Aires. Gobernación. Comision de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomia; Argentina

The Local Bubble (LB), a volume of roughly 100 pc radius filled with ionized gas of high temperature and low density, is not a unique object. It is obviously surrounded by several interstellar bubbles of similar properties. Some of them are as close as to undergo interaction with the LB. Our most prominent neighbour is the Loop I superbubble formed by the Sco-Cen OB association. It is shown that this huge shell is in collision with our Local Bubble. The product of this interaction is an annular cloud of dense neutral gas at the boundary between the two bubbles. Other examples for close neighbouring bubbles are the Gum nebula, the Eridanus bubble and possibly the two radio loops II and III.

An analysis of proper motion measurements of the Young Stellar Objects (YSOs) associated with the Cometary Globules (CGs) in the Gum Nebula is presented. While earlier studies based on the radial velocity measurements of the CGs suggested expansion of the system of the CGs, the observed proper motion of the YSOs shows no evidence for expansion. In particular the kinematics of two YSOs embedded in CGs is inconsistent with the supernova explosion of the companion of $\zeta$ Pup about 1.5 Myr ago as the cause of the expansion of the CG system. YSOs associated with the CGs share the average proper motion of the member stars of the Vela OB2 association. A few YSOs that have relatively large proper motions are found to show relatively low infrared excesses., Comment: 19 pages, 6 figures, 4 tables, Accepted for publication in MNRAS

It has been argued in the past that the ejecta of massive stars might explain the presence of shortlived nuclear species found in chondritic meteorites. The purpose of this paper is to provide new evidence in favor of such a picture. We will show that the Gum Nebula can be a good model for understanding the physical context in which our own solar system was born. This nebula is the sight of secondary low mass star formation induced by the massive stars at the center of the nebula. Recent theories of the propagation of stellar winds in the ISM (wind bubbles) and new models of massive stars, including detailed nucleosynthesis, allow one to follow in some detail the contamination process of the cometary globules by the ejecta of the massive stars located near the center of the nebula. We will show that the abundances of some short lived-species in chondritic meteorites are consistent with the amount that should be injected in the cometary globules of the Gum Nebula. The Gum Nebula is a region that offers the opportunity to understand stellar formation under simplified conditions.

We present photometric and spectroscopic results for the low mass pre-main sequence (PMS) stars with spectral types K - M in the cometary globule (CG) 30/31/38 complex. We obtained multi-object high resolution spectra for the targets selected as possible PMS stars from multi-wavelength photometry. We identified 11 PMS stars brighter than V = 16.5 with ages < 5 Myr at a distance of approximately 200 pc. The spatial distribution of the PMS stars, CG clouds, and ionizing sources (O stars and supernova remnants) suggests a possible triggered origin of the star formation in this region. We confirm the youth of the photometrically selected PMS stars using the lithium abundances. The radial velocities of the low mass PMS stars are consistent with those of the cometary globules. Most of the PMS stars show weak Halpha emission with W(Halpha) < 10 A. Only 1 out of the 11 PMS stars shows a moderate near-IR excess, which suggests a short survival time (t < 5 Myr) of circumstellar disks in this star forming environment. In addition, we find five young late type stars and one Ae star which have no obvious relation to the CG 30/31/38 complex. We also discuss a possible scenario of star formation history in the CG 30/31/38 region., 44 pages, 8 figures, AJ in press

We investigate the density structure of the interstellar medium using new high-resolution maps of the 8 micron, 24 micron, and 70 micron surface brightness towards a molecular cloud in the Gum Nebula, made as part of the Spitzer Space Telescope Galactic First Look Survey. The maps are correlated with 100 micron images measured with IRAS. At 24 and 70 micron, the spatial power spectrum of surface brightness follows a power law with spectral index -3.5. At 24 micron, the power law behavior is remarkably consistent from the 0.2 degree size of our maps down to the 5 arcsecond spatial resolution. Thus, the structure of the 24 micron emission is self-similar even at milliparsec scales. The combined power spectrum produced from Spitzer 24 micron and IRAS 25 micron images is consistent with a change in the power law exponent from -2.6 to -3.5. The decrease may be due to the transition from a two-dimensional to three-dimensional structure. Under this hypothesis, we estimate the thickness of the emitting medium to be 0.3 pc., Comment: 13 Pages, 3 Figures, to be published in Astrophysical Journal Supplement Series (Spitzer Special Issue), volume 154. Uses aastex v5.2

We have measured the scatter broadening of pulsars in the direction of the Gum nebula. For the first time, our observations show clear variations of scattering properties across the Gum nebula. The IRAS-Vela shell is shown to be a high scattering region. Our revised estimations of distances to these pulsars are consistently less by a factor of 2--3, which has very important consequences for the deduced values of radio luminosity and transverse velocity of pulsars., Astronomy & Astrophysics, 2001, 370, 586

We present a high resolution spectroscopic study of the ionised gas in Puppis-Vela, which includes the Gum Nebula and the IRAS Vela Shell, in the emission lines of Halpha lambda6563 angstrom, [NII] lambdalambda6548, 6584 angstrom and the [OIII] lambda5007 angstrom. Line profiles were obtained at 18 positions well distributed over the entire region. Only the [NII] line profiles in the region of the IRAS Vela Shell show double peaked profiles, consistent with an expansion velocity of 10 +/- 2km s-1. The ionised gas associated with the 36-degrees-diameter Gum Nebula does not show any such systematic motions. This is consistent with, and provides further confirmation of, the results obtained from the IRAS Super Sky Flux (ISSA) maps (Srinivasan Sahu & Blaauw 1993) that the IRAS Vela Shell and the Gum Nebula are two separate structures but seen overlapping in projection. We detected no [OIII] lambda5007angstrom emission in any of the positions observed. From the [NII]/Halpha ratio, the temperatures derived at the 18 positions vary between 5,000 to 12,0000 K.

An analysis of structure in rotation measure (RM) across the sky based on the RM catalog of Taylor et al. (2009) is presented. Several resolved RM structures are identified with structure in the local ISM, including radio loops I, II, and III, the Gum nebula, and the Orion-Eridanus super bubble. Structure functions (SFs) of RM are presented for selected areas, and maps of SF amplitude and slope across the sky are compared with H-alpha intensity and diffuse polarized intensity. RM variance on an angular scale of 1 degree is correlated with length of the line of sight through the Galaxy, with a contribution from local structures. The slope of the SFs is less concentrated to the Galactic plane and less correlated with length of the line of sight through the Galaxy, suggesting a more local origin for RM structure on angular scales ~ 10 degrees. The RM variance is a factor ~2 higher towards the SGP than towards the NGP, reflecting a more wide-spread asymmetry between the northern and southern Galactic hemispheres. Depolarization of diffuse Galactic synchrotron emission at latitudes < 30 degrees can be explained largely by Faraday dispersion related to small-scale variance in RM, but the errors allow a significant contribution from differential Faraday rotation along the line of sight., 13 pages, 14 figures. Figures 1-4 and 9-10 available as separate files. Accepted for publication in the Astrophysical Journal A complete pdf with all figures included is available at http://www.ras.ucalgary.ca/~stil/Stil_2010_RM_structure.pdf

We present the following observations of Wra 220, the H-alpha emission line star seen superposed on cometary globule 22 (CG22) on the ESO-SERC IIIaJ plates: (1) low resolution blue and red spectra (2) high resolution spectra in the region of the H-alpha 6563 angstrom line (3) near-IR photmetry (4) visual photometry from CCD images (5) IRAS Point Source Catalogue (PSC) data. Based on these data, we conclude that Wra 220 is a T-Tauri star (spectral type K2-K3) physically associated with CG22. Other properties of the star like luminosity class, spectral energy distribution, etc. have also been derived.

The IRAS Vela shell was first seen as a ring of infrared emission in the IRAS maps of the Gum-Vela region coincident with the Gum Nebula. We have studied the kinematics of the molecular material (12CO) associated with the IRAS point sources and Southern Dark Clouds seen in this region and established the presence of a giant expanding shell of molecular gas. The estimated mass, size and expansion velocity of the shell lead us to conclude that it is the remnant of a GMC, in the process of disintegration through the influence of a central OB association. We conjecture that the IRAS Vela shell is a nearby example of a “super shell” in its early stages of evolution and as such is an ideal opportunity to study these objects now widely seen both in our Galaxy and in new observations of the Magellanic Clouds.

The Gum Nebula, with a diameter of 36" and surrounded by Hα filaments, is one of the more extended features on the sky. Within that region several interesting objects as Vela, Puppis and RCW 38, are found. For this reason we decided to map this extended region with high sensitivity at the frequency of 1435 MHz. A reduction method was developed that allowed to calibrate absolutely the observations and to obtain the Spectral Index (Tb=f⁻ᵇ), comparing our observations with those obtained by Haslam et al. (1982)., Asociación Argentina de Astronomía

The first part of the thesis deals with the development of a wide-band mechanically tuned local oscillator using the Gunn diode for use with the 10.4m millimeter-wave radio telescope at the Raman Research Institute. This provides sufficient power to efficiently operate two cryogenic Schottky mixers (dual polarisation) and tunes over the frequency range 75-115 GHz covering most of the 3-mm atmospheric transmission window (W-band). Rotational transitions of many astrophysically important molecules including CO fall in this range. A study of the cometary globulesCGs in the Gum Nubula forms the second part. The CGs are characterised by compact, dusty heads with long faintly luminous tails extending on one side and narrow bright rims on the other side. There exists a significant population of such CGs in the Gum Nebula, distributed over a region ~80 parsec in radius with their tails pointing away from an apparent common center. Some of the heads have embedded young stars. In the region bounded by the CGs there are a few massive hot stars including zeta Puppis believed to be the most luminous star in the southern sky. It has been suspected that the morphological appearance of the CGs may be due to the influence of these stars. In order to understand the kinematics and the origin of the system, a study was undertaken using the first rotational transition of the carbon monoxide molecule. The study consisted of 12CO observations of the heads and the tails of the CGs. In addition, the Globule No.22 was mapped in both 12CO and 13CO. An analysis of this data has led to the following findings: 1. The system of CGs is expanding with respect to a common morphological center at ~12 kms-1. The expansion age is ~6 Myr. 2. Some of the tails observed show systematic velocity gradients. If the tails were formed due to the elongation resulting from these velocity gradients then the estimated stretching age is ~3 Myr. In order to clarify if externally triggered star formation is going on in this region, an analysis of the locations of the embedded young stellar objects (YSOs, identified from the Infra-Red Astronomy Satellite data) in the dark clouds in the Gum-Vela region was undertaken. This study has shown that the YSOs have a statistically significant tendency to fall on the sides of dark clouds facing the morphological center rather than the far sides, supporting external triggering. From the above analysis we come to the following conclusions: 1. The rough agreement between the expansion age and the tail-stretching age suggests a common origin for the expansion and the formation of the tails. The presence of young stars of comparable ages in the heads of some of the globules suggests that the processes responsible for the expansion may have also triggered star formation in them. 2. The radiation pressure from the hot stars in the central region or the stellar winds from them cannot account for the momentum of the expanding globules. It is more likely that the rocket effect arising out of the heating and the consequent anisotropic ablation of the globules supplied the necessary momentum. From the space motion of the star zeta Puppis we suggest that it had a massive companion which exploded as a supernova half a million years ago. The combined effect of the ultra-violet radiation and the stellar wind from this binary as well as from other stars in the neighbourhood significantly affected the parent molecular cloud in which they formed. This resulted in much of the molecular material in the vicinity being blown away except the numerous regions of enhanced density (condensations) in the original molecular cloud. Continued effect of the radiation and stellar winds resulted in these condensations being set in motion, as well as developing cometary tails.

The present quantitative model for Galactic free electron distribution abandons the assumption of axisymmetry and explicitly incorporates spiral arms; their shapes and locations are derived from existing radio and optical observations of H II regions. The Gum Nebula's dispersion-measure contributions are also explicitly modeled. Adjustable quantities are calibrated by reference to three different types of data. The new model is estimated to furnish distance estimates to known pulsars that are accurate to about 25 percent.

The data from six high-dispersion IUE echelle spectra are averaged in order to obtain an interstellar absorption line spectrum with an S/N of about 30 and a resolution of about 25 km/s. The interstellar lines of C IV and Si IV are very strong and broad and N V is detected. The profiles for these species and Al III are compared to the Copernicus satellite profiles for O VI. The high ionization lines toward HD 64760 are much stronger and broader than those recorded toward Zeta Pup and Gamma super 2 Vel, the two exciting stars of the Gum nebula. The profiles for Al III and Si IV are similar and considerably narrower than the O VI profile. An origin in photoionized Gum nebula gas is suggested as the most likely explanation for Al III and Si IV. The C IV profile has a high positive velocity wing extending to approximately +80 km/s, which is similar in appearance to the positive velocity portion of the O VI profile. It is inferred that a substantial part of the observed C IV has an origin in the collisionally ionized gas most likely rsponsible for the O VI.

Observations of a speckle hologram of scattering material along the line of sight to the Vela pulsar indicate that this material is concentrated in the Vela supernova remnant, deep within the Gum Nebula. The speckle hologram is observed through the amplitude and phase variations of the interferometric cross-power spectrum with time and frequency. These variations describe the density fluctuations of the interstellar plasma, in a holographic fashion. The decorrelation due to the phase variations of the speckles yields the angular size of the scattering disk; comparison with the bandwidth of their amplitude variations yields a characteristic distance from earth to the scattering material of 0.81 +/- 0.03 of the distance from earth to the pulsar. This result is consistent with theories of irregularities associated with particle acceleration in shocks in supernova remnants.

The Gum Nebula was observed by the A-2 LED proportional counters on the HEAO-1 satellite as part of the all-sky survey. The first detection of X-ray emission associated with the Gum Nebula is reported. Soft X-ray spectra were constructed from the A-2 LED PHA data. Single temperature Raymond-Smith models were fitted to the observed spectra to yield temperature, column density and emission measure. The temperature is 6 x 10 exp 5 K, the column density 4 x 10 exp 20/sq cm, and the emission measure 5 cm exp-6 pc. The X-ray and optical properties of the Gum Nebula are consistent with a supernova remnant in the shell stage of evolution, which was the product of an energetic (3 x 10 exp 51 ergs) supernova explosion which occurred about 2 x 10 exp 6 yr ago.

Photographic and spectroscopic observations are presented of some faint nebulosity which is associated with the strong IRAS point source 08211 - 4158. Two components are observed. One relatively compact and knotty region has a purely gaseous spectrum characteristic of a low-excitation Herbig-Haro object, while another area shows a spectrum with strong continuum radiation and superposed emission lines which suggest that it is scattering light from an embedded young star. Radial-velocity measurements show that this star is at rest with respect to its surroundings while the Herbig-Haro object has a mean velocity of -38 km/s with respect to its local standard of rest. The evidence favors but does not conclusively show that the source 1 in the area, identified by Campbell and Persson (1988), marks the position of the embedded star which powers the Herbig-Haro object.

The origin of the local interstellar matter, especially the hot component, is studied. The bulk of the local interstellar space is occupied with hot low-density matter, which is similar to the gas heated by the shock front of the supernova remnant. We investigate the model that our Sun is located in a superbubble. The superbubbles are observed in Orion-Eridanus region and Gum nebula. The similar objects are found in λ 21 cm H I maps as H I shells and holes. The superbubbles certainly correlate with OB associations and giant molecular clouds. The evolution of superbubbles formed by sequential supernova explosions in an OB association is studied by hydrodynamical simulations. We compare the results with observations. A model of cycling of interstellar matter is presented, in relation to the evolution of the superbubble.

The Gum Nebula is seen on photographs of the southern skies as an extensive region of ionized hydrogen that surrounds the well known Vela X supernova remnant. One of the largest objects in our galaxy, the Nebula was first recognized as a single emission complex by Colin S. Gum during the 1950's. Until recently, astronomers assumed that it was a “Stromgren sphere,” excited by ultraviolet light from the hot stars gamma Velorum and zeta Puppis within it. This excitation process accounts for the Orion Nebula and other H‐II regions. The synchrotron and thermal bremsstrahlung mechanisms account for the radiation from supernova remnants, such as the Crab Nebula and Vela X; these objects consist of rapidly expanding matter ejected by the supernova explosions.