Weak Radio Source Research Articles

SPT-CL J2215−3537: A Massive Starburst at the Center of the Most Distant Relaxed Galaxy Cluster

We present the discovery of the most distant, dynamically relaxed cool core cluster, SPT-CL J2215−3537 (SPT2215), and its central brightest cluster galaxy (BCG) at z = 1.16. Using new X-ray observations, we demonstrate that SPT2215 harbors a strong cool core with a central cooling time of 200 Myr (at 10 kpc) and a maximal intracluster medium cooling rate of 1900 ± 400 M ⊙ yr−1. This prodigious cooling may be responsible for fueling the extended, star-forming filaments observed in Hubble Space Telescope imaging. Based on new spectrophotometric data, we detect bright [O ii] emission in the BCG, implying an unobscured star formation rate (SFR) of M ⊙ yr−1. The detection of a weak radio source (2.0 ± 0.8 mJy at 0.8 GHz) suggests ongoing feedback from an active galactic nucleus (AGN), though the implied jet power is less than half the cooling luminosity of the hot gas, consistent with cooling overpowering heating. The extreme cooling and SFR of SPT2215 are rare among known cool core clusters, and it is even more remarkable that we observe these at such high redshift, when most clusters are still dynamically disturbed. The high mass of this cluster, coupled with the fact that it is dynamically relaxed with a highly isolated BCG, suggests that it is an exceptionally rare system that must have formed very rapidly in the early universe. Combined with the high SFR, SPT2215 may be a high-z analog of the Phoenix cluster, potentially providing insight into the limits of AGN feedback and star formation in the most massive galaxies.

Discovery of a Giant Radio Fossil in the Ophiuchus Galaxy Cluster

Abstract The Ophiuchus galaxy cluster exhibits a curious concave gas density discontinuity at the edge of its cool core. It was discovered in the Chandra X-ray image by Werner and collaborators, who considered the possibility of it being a boundary of an active galactic nucleus (AGN)-inflated bubble located outside the core, but discounted this possibility because it required much too powerful an AGN outburst. Using low-frequency (72–240 MHz) radio data from the Murchison Widefield Array/GLEAM and the Giant Metrewave Radio Telescope, we found that the X-ray structure is, in fact, a giant cavity in the X-ray gas filled with diffuse radio emission with an extraordinarily steep radio spectrum. It thus appears to be a very aged fossil of the most powerful AGN outburst seen in any galaxy cluster (pV ∼ 5 × 1061 erg for this cavity). There is no apparent diametrically opposite counterpart either in X-ray or in the radio. It may have aged out of the observable radio band because of the cluster asymmetry. At present, the central AGN exhibits only a weak radio source, so it should have been much more powerful in the past to have produced such a bubble. The AGN is currently starved of accreting cool gas because the gas density peak is displaced by core sloshing. The sloshing itself could have been set off by this extraordinary explosion if it had occurred in an asymmetric gas core. This dinosaur may be an early example of a new class of sources to be uncovered by low-frequency surveys of galaxy clusters.

The fast molecular outflow in the Seyfert galaxy IC 5063 as seen by ALMA

We use high-resolution (0.5 arcsec) CO(2-1) observations performed with ALMA to trace the kinematics of the molecular gas in the Seyfert 2 galaxy IC5063. A fast outflow of molecular gas extends along the entire radio jet, with the highest outflow velocities about 0.5kpc from the nucleus, at the location of the brighter hot-spot in the W lobe. The data show that a massive, fast outflow with velocities up to 650 km/s of cold molecular gas is present, in addition to one detected earlier in warm H2, HI and ionised gas. Both the central AGN and the radio jet could energetically drive the outflow. However, the characteristics of the outflowing gas point to the radio jet being the main driver. This is important, because IC5063, although one of the most powerful Seyfert galaxies, is a relatively weak radio source (P = 3x10^23 W/Hz). All the observed characteristics can be described by a scenario of a radio plasma jet expanding into a clumpy medium, interacting directly with the clouds and inflating a cocoon that drives a lateral outflow into the interstellar medium. This model is consistent with results obtained by recent simulations such as those of Wagner et al.. A stronger, direct interaction between the jet and a gas cloud is present at the location of the brighter W lobe. Even assuming the most conservative values for the conversion factor CO-to-H2, the mass of the outflowing gas is between 1.9 and 4.8x10^7 Msun. These amounts are much larger than those of the outflow of warm gas (molecular and ionized) and somewhat larger than of the HI outflow. This suggests that most of the observed cold molecular outflow is due to fast cooling after being shocked. This gas is the end product of the cooling process. Our CO observations demonstrate that fast outflows of molecular gas can be driven by relativistic jets.

AN HST /WFC3-UVIS VIEW OF THE STARBURST IN THE COOL CORE OF THE PHOENIX CLUSTER

We present Hubble Space Telescope Wide Field Camera 3 observations of the core of the Phoenix Cluster SPT-CLJ2344-4243 in five broadband filters spanning rest-frame 1000--5500A. These observations reveal complex, filamentary blue emission, extending for >40kpc from the brightest cluster galaxy. We observe an underlying, diffuse population of old stars, following an r^1/4 distribution, confirming that this system is somewhat relaxed. The spectral energy distribution in the inner part of the galaxy, as well as along the extended filaments, is a smooth continuum and is consistent with that of a star-forming galaxy, suggesting that the extended, filamentary emission is not due to the central AGN, either from a large-scale ionized outflow or scattered polarized UV emission, but rather a massive population of young stars. We estimate an extinction-corrected star formation rate of 798 +/- 42 Msun/yr, consistent with our earlier work based on low spatial resolution ultraviolet, optical, and infrared imaging. The lack of tidal features and multiple bulges, combine with the need for an exceptionally massive (>10^11 Msun) cold gas reservoir, suggest that this star formation is not the result of a merger of gas-rich galaxies. Instead, we propose that the high X-ray cooling rate of ~2700 Msun/yr is the origin of the cold gas reservoir. The combination of such a high cooling rate and the relatively weak radio source in the cluster core suggests that feedback has been unable to halt cooling in this system, leading to this tremendous burst of star formation.

A VLA search for young protostars embedded in dense cores

Aims.Four dense cores, L1582A, L1689A, B133 and B68, classified as prestellar in terms of the absence of detectable NIR emission, are observed at radio wavelengths to investigate whether they nurture very young protostars. Methods.We perform deep radio continuum observations at 3.6 cm and 6 cm using the VLA. Results.No definite young protostars were discovered in any of the four cores observed. A few radio sources were discovered close to the observed cores, but these are most likely extragalactic sources or YSOs unrelated to the cores observed. In L1582A we discovered a weak radio source near the centre of the core with radio characteristics and offset from the peak of the submillimeter emission similar to that of the newly discovered protostar in the core L1014, indicating a possible protostellar nature for this source. This needs to be confirmed with near- and/or mid-infrared observations (e.g. with Spitzer). Hence based on the current observations we are unable to confirm unequivocally that L1582A is starless. In L1689A a possible 4.5-$\sigma$ radio source was discovered at the centre of the core, but needs to be confirmed with future observations. In B133 a weak radio source, possibly a protostar, was discovered at the edge of the core on a local peak of the core submm emission, but no source was detected at the centre of the core. Thus, B133 is probably starless, but may have a protostar at its edge. In B68 no radio sources were discovered inside or at the edge of the core, and thus B68 is indeed starless. Four more radio sources with spectral indices characteristic of young protostars were discovered outside the cores but within the extended clouds in which these cores reside. Conclusions.We conclude that the number of cores misclassified as prestellar is probably very small and does not significantly alter the estimated lifetime of the prestellar phase.

The Faint Optical Afterglow and Host Galaxy of GRB 020124: Implications for the Nature of Dark Gamma‐Ray Bursts

We present ground-based optical observations of GRB 020124 starting 1.6 hours after the burst, as well as subsequent Very Large Array (VLA) and Hubble Space Telescope (HST) observations. The optical afterglow of GRB 020124 is one of the faintest afterglows detected to date, and it exhibits a relatively rapid decay, $F_\nu\propto t^{-1.60\pm 0.04}$, followed by further steepening. In addition, a weak radio source was found coincident with the optical afterglow. The HST observations reveal that a positionally coincident host galaxy must be the faintest host to date, R>29.5 mag. The afterglow observations can be explained by several models requiring little or no extinction within the host galaxy, A_V~0-0.9 mag. These observations have significant implications for the statistics of the so-called dark bursts (bursts for which no optical afterglow is detected), which are usually attributed to dust extinction within the host galaxy. The faintness and relatively rapid decay of the afterglow of GRB 020124, combined with the low inferred extinction indicate that some dark bursts are intrinsically dim and not dust obscured. Thus, the diversity in the underlying properties of optical afterglows must be observationally determined before substantive inferences can be drawn from the statistics of dark bursts.

Heartbeat of the Mouse: A Young Radio Pulsar Associated with the Axisymmetric Nebula G359.23−0.82

We report the discovery of PSR J1747-2958, a radio pulsar with period P = 98 ms and dispersion measure DM = 101 cm-3 pc, in a deep observation with the Parkes telescope of the axially symmetric radio nebula (G359.23-0.82). Timing measurements of the newly discovered pulsar reveal a characteristic age P/2 = 25 kyr and spin-down luminosity = 2.5 × 1036 ergs s-1. The pulsar (timing) position is consistent with that of the Mouse's head. The distance derived from the DM (≈2 kpc) is consistent with the Mouse's distance limit from H I absorption (<5.5 kpc). Also, the X-ray energetics of the Mouse are compatible with being powered by the pulsar. Therefore, we argue that PSR J1747-2958, moving at supersonic speed through the local interstellar medium, powers this unusual nonthermal nebula. The pulsar is a weak radio source, with a period-averaged flux density at 1374 MHz of 0.25 mJy and a luminosity of ~1 mJy kpc2.

Discovery of a 136 Millisecond Radio and X-Ray Pulsar in Supernova Remnant G54.1+0.3

We report the discovery of a pulsar with period P = 136 ms and dispersion measure 308 cm(-3) pc in a deep observation of the supernova remnant (SNR) G54.1+0.3 with the Arecibo radio telescope. Timing measurements of the new pulsar, J1930+1852, reveal a characteristic age of P/2 (P) over dot = 2900 yr and a spin-down luminosity of (E) over dot = 1.2 x 10(37) ergs s(-1). We have subsequently searched archival ASCA X-ray data of this SNR and detect pulsations with a consistent period. These findings ensure that PSR J1930+1852 is the pulsar that powers the Crab-like SNR G54.1+0.3. Together with existing Chandra observations of the SNR, we derive an X-ray pulsed fraction (2-10 keV) of approximate to27%. We also find that the cooling efficiency of the pulsar wind nebula (PWN) is intermediate between those of the Vela and Crab PWNe: L-x(2-10 keV) similar to0.002 (E) over dot. PSR J1930+1852 is a very weak radio source, with a period-averaged flux density at 1180 MHz of 60 muJy. For a distance of 5 kpc, its luminosity, similar to1 mJy kpc(2), is among the lowest for known young pulsars.

ChandraX‐Ray Observations of the Spiral Galaxy M81

A Chandra X-Ray Observatory ACIS-S imaging observation is used to study the population of X-ray sources in the nearby Sab galaxy M81 (NGC 3031). A total of 177 sources are detected with 124 located within the D25 isophote to a limiting X-ray luminosity of ~3 × 1036 ergs s-1. Source positions, count rates, luminosities in the 0.3-8.0 keV band, limiting optical magnitudes, and potential counterpart identifications are tabulated. Spectral and timing analysis of the 36 brightest sources are reported including the low-luminosity active galactic nucleus, SN 1993J, and the Einstein-discovered ultraluminous X-ray source X6. The nucleus accounts for ~86%, or 5 × 1040 ergs s-1, of the total X-ray emission from M81. Its spectrum is well fitted by an absorbed power law with photon index 1.98 ± 0.08, consistent with previous observations (average index 1.9). SN 1993J has softened and faded since its discovery. At an age of 2594 days, SN 1993J displayed a complex thermal spectrum from a reverse shock rich in Fe L and highly ionized Mg, Si, and S but lacking O. A hard X-ray component, emitted by a forward shock, is also present. X6 is spatially coincident with a stellar object with optical brightness and colors consistent with an O9-B1 main-sequence star. It is also coincident with a weak radio source with a flux density of ~95 μJy at λ = 3.6 cm. The continuum-dominated X-ray spectrum of X6 is most closely reproduced by a blackbody disk model suggesting the X-ray source is an ~18 M☉ object accreting at nearly its Eddington limit.

Discovery of Radio Pulsations from the X-Ray Pulsar J0205+6449 in Supernova Remnant 3C 58 with the Green Bank Telescope

We report the discovery with the 100m Green Bank Telescope of 65 ms radio pulsations from the X-ray pulsar J0205+6449 at the center of supernova remnant 3C58, making this possibly the youngest radio pulsar known. From our observations at frequencies of 820 and 1375 MHz, the free electron column density to USSR J0205+6449 is found to be 140.7 +/- 0.3/cc pc. The barycentric pulsar period P and P(dot) determined from a phase-coherent timing solution are consistent with the values previously measured from X-ray observations. The averaged radio profile of USSR J0205+6449 consists of one sharp pulse of width = 3 ms = 0.05 P. The pulsar is an exceedingly weak radio source, with pulse-averaged flux density in the 1400 MHz band of approximately 45 micro-Jy and a spectral index of approximately -2.1. Its radio luminosity of approximately 0.5 may kpc(exp 2) at 1400 MHz is lower than that of approximately 99% of known pulsar and is the lowest among known young pulsars.

Hard X-ray and Metric/Decimetric Radio Observations of the 20 February 2002 Solar Flare

The GOES C7.5 flare on 20 February 2002 at 11:07 UT is one of the first solar flares observed by RHESSI at X-ray wavelengths. It was simultaneously observed at metric/decimetric wavelengths by the Nancay radioheliograph (NRH) which provided images of the flare between 450 and 150 MHz. We present a first comparison of the hard X-ray images observed with RHESSI and of the radio emission sites observed by the NRH. This first analysis shows that: (1) there is a close occurrence between the production of the HXR-radiating most energetic electrons and the injection of radio-emitting non-thermal electrons at all heights in the corona, (2) modifications with time in the pattern of the HXR sources above 25 keV and of the decimetric radio sources at 410 MHz are observed occurring on similar time periods, (3) in the late phase of the most energetic HXR peak, a weak radio source is observed at high frequencies, overlying the EUV magnetic loops seen in the vicinity of the X-ray flaring sites above 12 keV. These preliminary results illustrate the potential of combining RHESSI and NRH images for the study of electron acceleration and transport in flares.

HST imaging of an old galaxy group at z=1.55

We present high-resolution imaging in the rest-frame optical of the weak radio source LBDS53W091 (Windhorst, van Heerde and Katgert: 1984, AA Spinrad et al.: 1997, ApJ 484, 581). We have obtained deep Hubble Space Telescope imaging over 10 orbits with NICMOS (Thompson et al.: 1998, ApJLett 492, 95), using camera 2 with the F160W H-band filter (l.6μm) which is a good approximation to the rest-frame R-band. Our observations reveal a radial light profile which is well fit by a de Vaucouleurs r 1/4 law, with a scale length of r e = 0.3″ (2.3h 70 −1 kpc for Ω M = 0.3 and ΩΛ = 0). The elliptical morphology of the radio galaxy indicates a dynamically-evolved old system (consistent with the spectroscopic results). Some surrounding objects lie on the color:magnitude relation for a cluster at z = 1.55, and are likely to be associated. The group of galaxies are somewhat more luminous than the fundamental plane of ellipticals (Djorgovski and Davis: 1987, ApJ 313, 59; Dressler et al.: 1987, ApJ 313, 42) at z = 0 subject to (1 + z)4 surface brightness dimming, but are consistent with estimates of the fundamental plane at high redshift subject to passive luminosity evolution from a formation epoch of z > 3 (e.g., van Dokkum et al.: 1998, ApJLett 504, 17).

Diffuse Gas and Low‐Mass X‐Ray Binaries in theChandraObservation of the S0 Galaxy NGC 1553

We have spatially and spectrally resolved the sources of X-ray emission from the X-ray-faint S0 galaxy NGC 1553 using an observation from the Chandra X-Ray Observatory. The majority (70%) of the emission in the 0.3-10.0 keV band is diffuse, and the remaining 30% is resolved into 49 discrete sources. Most of the discrete sources associated with the galaxy appear to be low-mass X-ray binaries (LMXBs). The luminosity function of the LMXB sources is well fitted by a broken power law with a break luminosity comparable to the Eddington luminosity for a 1.4 M☉ neutron star. It is likely that those sources with luminosities above the break are accreting black holes, and those below are mostly neutron stars in binary systems. Spectra were extracted for the total emission, diffuse emission, and sum of the resolved sources; the spectral fits for all require a model including both a soft and hard component. The diffuse emission is predominately soft, while the emission from the sources is mostly hard. Approximately 24% of the diffuse emission arises from unresolved LMXBs, with the remainder resulting from thermal emission from hot gas. There is a very bright source at the projected position of the nucleus of the galaxy. The spectrum and luminosity derived from this central source are consistent with it being an active galactic nucleus (AGN); the galaxy also is a weak radio source. Finally, the diffuse emission exhibits significant substructure with an intriguing spiral feature passing through the center of the galaxy. The X-ray spectrum and surface brightness of the spiral feature are consistent with adiabatic or shock compression of ambient gas but not with cooling. This feature may be due to compression of the hot interstellar gas by radio lobes or jets associated with the AGN.

An Excited H2Disk and the Core Structure of the Extraordinary Bipolar Planetary Nebula KjPn 8

A disk of excited H2v=1 → 0 S(1) (2.122 μm) emission has been found in the core of the extraordinary bipolar planetary nebula KjPn 8. This surrounds the central, extended, and clumpy thermal radio emission (VLA) and near-infrared (J, H, and K' bands) source. The H2 disk is found to be contained within a previously found expanding CO disk, and they share the same orientation. The plane of the H2 disk is perpendicular to the high-velocity bipolar outflows. The 4'' diameter core of KjPn 8 has also been observed for 37 on-source hours at a wavelength of 6 cm with the MERLIN radio interferometer with an angular resolution of 005. The data have been combined with 4 hr of VLA-A observations at the same wavelength but where the resolution is 05. The most remarkable feature of these radio observations is the possible presence of a weak radio source embedded in the center of the H2 disk. It is thought plausible that this point source may be direct emission from the powerful, ionized wind of the central star that now drives this nebulosity.

LBDS 53W091: An Old, Red Galaxy atz= 1.552

The weak radio source LBDS 53W091 is associated with a very faint (R approx. 24.5) red (R-K approx. 5.8) galaxy. Long spectroscopic integrations with the W. M. Keck telescope have provided an absorption-line redshift, z=1.552 +/- 0.002. The galaxy has a rest frame ultraviolet spectrum very similar to that of an F6V star, and a single-burst old stellar population that matches the IR colors, the optical energy distribution and the spectral discontinuities has a minimum age of 3.5 Gyr. We present detailed population synthesis analyses of the observed spectrum in order to estimate the time since the last major epoch of star formation. We discuss the discrepancies in these estimates resulting from using different models, subjecting the UV spectrum of M32 to the same tests as a measure of robustness of these techniques. The models most consistent with the data tend to yield ages at z=1.55 of >3.5Gyr, similar to that inferred for the intermediate-age population in M32. Depending upon the assumed Hubble constant and the value of Omega_0, only certain cosmological expansion times are consistent with the age of LBDS 53W091; in particular, for Omega_0=1, only models with H_0 < 45 km/s/Mpc are permitted. For H_0=50 km/s/Mpc and Omega_0=0.2, we derive a formation redshift, z_f >= 5.

The dynamic interstellar medium in NGC 4438

We present multiwavelength observations of the interstellar medium in the disturbed galaxy NGC 4438. We find extended emission-line filaments, which are kinematically unrelated to the galaxy disk. For one of these features, an extended loop, we propose a scheme in which the 'bubble' seen at radio wavelengths has swept a clear path for outflowing material from the nucleus to ionize more distant material. Another radial emission-line feature might represent shocks in the disk along a gravitationally-defined caustic produced during a tidal encounter, or a 'searchlight beam' escaping the inner dusty regions of the galaxy. Energy-balance arguments favor the shock picture, but further study will be important in understanding this feature. Emission-line ratios indicate that shocks may be important in the energetics of the interstellar medium (ISM) through much of the disk of NGC 4438; the alternative is star formation in a uniformly very dense ISM. We use K-band data to locate the stellar peak of the galaxy, which is just outside the prominent radio-continuum loop or shell feature. The nucleus itself is at most a very weak radio source. However, the more extended radio structure shows that energetic events have taken place in the innermost few hundred parsees of NGC 4438. The interstellar medium of NGC 4438 may show at once the impact of nuclear energy input (from an AGN or cocooned starburst), perturbation by the companion NGC 4435, and interaction with the dense intergalactic medium in the Virgo core.

VLA observations of 1E 1740.7-2942 - A search for radio recombination lines of positronium

view Abstract Citations (11) References (44) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS VLA Observations of 1E 1740.7-2942: A Search for Radio Recombination Lines of Positronium Anantharamaiah, K. R. ; Dwarakanath, K. S. ; Morris, D. ; Goss, W. M. ; Radhakrishnan, V. Abstract We have searched for the Ps87-alpha recombination line of positronium at the position of the Einstein X-ray source 1E 1740.7-2942 which has been identified as a strong source of time-variable annihilation line radiation. No line was detected with a 3 sigma upper limit of 330 microJy for a line width of 23.5 MHz, the expected width if the temperature of the annihilation region is about 7 x 10 exp 4 K. A continuum image of the field made from the same data shows, within the 90 percent confidence error circle of the X-ray source, a weak radio source with a core and lobe structure similar to extragalactic double radio sources. Comparison with other observations shows that the radio flux density of the core at 6 cm had increased by a factor of about 2.6 between 1991 October 7 and November 16 and has been decreasing steadily since then. We have explored some possible relations between the radio source and the X-ray source. We find that the radio and the X-ray sources could well be associated with each other. The nature of this source is uncertain - it could be either Galactic or extragalactic. In either case this source is a unique object. Publication: The Astrophysical Journal Pub Date: June 1993 DOI: 10.1086/172730 Bibcode: 1993ApJ...410..110A Keywords: Positronium; Radio Spectra; Recombination Reactions; Very Large Array (Vla); X Ray Sources; Galactic Nuclei; Milky Way Galaxy; Astronomy; BLACK HOLE PHYSICS; ELEMENTARY PARTICLES; GALAXY: CENTER; GAMMA RAYS: OBSERVATIONS full text sources ADS | data products SIMBAD (2) NED (1)

H I observations of three IRAS detected elliptical galaxies

view Abstract Citations (21) References (56) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS H i Observations of Three IRAS Detected Elliptical Galaxies Walsh, D. E. P. ; van Gorkom, J. H. ; Bies, W. E. ; Katz, N. ; Knapp, G. R. ; Wallington, S. Abstract Three elliptical galaxies with strong far-infrared emission (IRAS flux density greater than 1 Jy at 100 microns) were observed in the H I 21 cm line with the VLA. Only one of these, the dwarf NGC 855, was detected. This galaxy has an extended H I distribution which is highly inclined to the optical major axis and a weak radio continuum source. Deep optical images show complex structure in the inner regions and emission lines suggestive of star formation. It is likely that this star formation and the cool interstellar medium (ISM) are sources for the far-IR luminosity. IC 1459 is in a group containing several spirals and shows signs of recent interaction. Neutral hydrogen was not detected, but there is a powerful central radio continuum source, and the 100 micron emission is plausibly explained as arising from this source. NGC 6958 has only weak radio continuum emission, and the lower limit on L_IR_/M_HI_ is at the high end of the range for this quantity among ellipticals. It is likely that a small amount of dust heated by a strong radiation field is providing the far- infrared luminosity. The infrared properties of these galaxies are similar, but the IR emission seems to have three different origins, complicating the interpretation of IRAS data for ellipticals. Publication: The Astrophysical Journal Pub Date: April 1990 DOI: 10.1086/168556 Bibcode: 1990ApJ...352..532W Keywords: Elliptical Galaxies; Infrared Astronomy Satellite; Infrared Sources (Astronomy); Neutral Gases; Radio Sources (Astronomy); Very Large Array (Vla); Data Reduction; Flux Density; H Lines; Hydrogen; Interstellar Matter; Spiral Galaxies; Astrophysics; GALAXIES: INTERACTIONS; INFRARED: SOURCES; RADIO SOURCES: GALAXIES; RADIO SOURCES: 21 CM RADIATION full text sources ADS | data products NED (8) SIMBAD (7)

S106-IRS4: A Star Loosing Mass in the Centre of a Bipolar Nebula

S106-IRS4 is the brightest near IR source associated with the S106 bipolar nebula. It is located exactly at the centre of the bipolar structure, inside the narrow gap of emission between the two radio lobes. It is also a weak radio source. An analysis of the near IR photometric measurements and of the radio fluxes suggests the presence of an ionized envelope produced by mass loss of the early type star which is responsible for the ionization of the nebula (Felli et al. 1984).

The enigma of RX Puppis

RX Puppis is a southern symbiotic star (R.A. 08h12m 28s.2, Dec. −41°33'18“ B1950). For almost a century it has been seen to have had a violent history at optical wavelengths. In 1974 it was discovered, at 5 GHz, to be a weak radio source. Shortly after, its radio spectrum was found to be of the optically thin type, having approximately the same flux density at all frequencies between 2.7 and 22 GHz. This implied that the RX Puppis system contained dispersed, ionized gas having a linear size &gt;1015 cm.