On 4 July 2005, many observatories around the world and in space observed the collision of Deep Impact with comet 9P/Tempel 1 or its aftermath. This was an unprecedented coordinated observational campaign. These data show that (i) there was new material after impact that was compositionally different from that seen before impact; (ii) the ratio of dust mass to gas mass in the ejecta was much larger than before impact; (iii) the new activity did not last more than a few days, and by 9 July the comet's behavior was indistinguishable from its pre-impact behavior; and (iv) there were interesting transient phenomena that may be correlated with cratering physics.

We have observed simultaneously with the VLA in its A configuration the 1.3 cm continuum and H₂O maser emission toward the star-forming region W75N(B) with 01 resolution using a powerful cross-calibration technique. Three continuum sources (VLA 1, VLA 2, and VLA 3) were detected in a region of 15. VLA 1 is elongated (043 × 012) approximately in the direction of the bipolar molecular outflow observed at scales of 2'. The frequency dependence of the flux density and size are consistent with an optically partially thick ionized thermal biconical jet. VLA 2 appears unresolved, while VLA 3 shows a bright core plus extended emission. We detected 29 H₂O maser spots (spatial components) in a region of 13'' × 7'' around W75N(B). These masers are mainly distributed in two clusters, one associated with VLA 1 (11 maser spots), and the other one associated with VLA 2 (eight maser spots). One H₂O maser spot is associated with VLA 3. The masers associated with VLA 1 are distributed along the major axis of the radio jet. We conclude that VLA 1 is the powering source of the extended bipolar molecular outflow and that the water masers along the radio jet axis are delineating the outflow at scales of 1''. On the other hand, the eight masers coincident with VLA 2 are distributed in a shell of 018 × 010, with a rough north-south velocity segregation that could indicate bound motions around this continuum source. From the comparison of H₂O and OH maser distribution in the region with respect to the three radio sources, we consider an evolutionary scheme in which H₂O masers are excited in gravitationally bound material (e.g., in circumstellar disks) in less evolved young stellar objects (YSOs), while in more evolved YSOs H₂O masers preferentially trace outflows.

As part of a systematic search programme of a 10° wide strip of the northern Galactic plane, we present preliminary evidence for the discovery of four (and possibly five) new supernova remnants (SNRs). The pilot search area covered the 19–20 h right ascension zone sampling from +20° to +55° in declination using binned mosaic images from the Isaac Newton Telescope Photometric Hα Survey (IPHAS). The optical identification of the candidate SNRs was based mainly on their filamentary and arc-like emission morphologies, their apparently coherent, even if fractured, structure and clear disconnection from any diffuse neighbouring H ii region type nebulosity. Follow-up optical spectroscopy was undertaken, sampling carefully across prominent features of these faint sources. The resulting spectra revealed typical emission-line ratios for shock-excited nebulae which are characteristic of SNRs, which, along with the latest diagnostic diagrams, strongly support the likely SNR nature of these sources: G038.7−1.3 (IPHASX J190640.5+042819), G067.6+0.9 (IPHASX J195744.9+305306), G066.0−0.0 (IPHASX J195749.2+290259) and G065.8−0.5 (IPHASX J195920.4+283740). A fifth possible younger, higher density nebula SNR candidate, G067.8+0.5 (IPHASX J200002.4+305035), was discovered ∼5 arcmin to the west of IPHASX J195744.9+305306, and it warrants further study. A multiwavelength cross-check from available archived data in the regions of these candidates was also performed with a focus on possible radio counterparts. A close positional match between previously unrecognized radio structures at several frequencies and across various components of the Hα optical image data was found for all SNR candidates. This lends further direct support for the SNR nature of these objects. Evolved SNRs may have very weak and/or highly fragmented radio emission which could explain why they had not been previously recognized, but the association becomes clear in combination with the optical emission.

A spectacular (14' × 4') bipolar nebula, with a symmetric and rotating, high-velocity collimated outflow, with episodic outburst properties, has been discovered in the Cassiopeia-Cepheus region. A compact object classified as the planetary nebula KjPn 8 is located at the center of symmetry of this extraordinary nebula. The angular extent of this bipolar structure is now the largest one known associated with a planetary nebula (PN). A mosaic of Hα images covering the full extent of the nebula is presented, as well as [N II] λ6584, [S II] λ6724, [O II] λ3729, and [O III] λ5007 images of the central (5' × 5') region. These images reveal symmetric pairs of bow shocks which are located at different position angles, in a way expected from a rotating, episodic jet. Low-dispersion spectroscopy of regions of the bipolar lobes confirms their shock-excited nature. The core is of low excitation class and seems nitrogen enriched. Our 3.5 cm VLA observations yield a first radio detection of the core of KjPn 8.

With its remarkable double-S shape, IC 4634 is an archetype of point-symmetric planetary nebulae (PN). In this paper, we present a detailed study of this PN using archival HST WFPC2 and ground-based narrow-band images to investigate its morphology, and long-slit spectroscopic observations to determine its kinematics and to derive its physical conditions and excitation. The data reveal new structural components, including a distant string of knots distributed along an arc-like feature 40"-60" from the center of the nebula, a skin of enhanced [O III]/H-alpha ratio enveloping the inner shell and the double-S feature, and a triple-shell structure. The spatio-kinematical study also finds an equatorial component of the main nebula that is kinematically independent from the bright inner S-shaped arc. We have investigated in detail the bow shock-like features in IC 4634 and found that their morphological, kinematical and emission properties are consistent with the interaction of a collimated outflow with surrounding material. Indeed, the morphology and kinematics of some of these features can be interpreted using a 3D numerical simulation of a collimated outflow precessing at a moderate, time-dependent velocity. Apparently, IC 4634 has experienced several episodes of point-symmetric ejections oriented at different directions with the outer S-shaped feature being related to an earlier point-symmetric ejection and the outermost arc-like string of knots being the relic of an even much earlier point-symmetric ejection. There is tantalizing evidence that the action of these collimated outflows has also taken part in the shaping of the innermost shell and inner S-shaped arc of IC 4634.