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We report the first evidence for high-mass star formation triggered by collisions of molecular clouds in M 33. Using the Atacama Large Millimeter/submillimeter Array, we spatially resolved filamentary structures of giant molecular cloud 37 in M 33 using 12CO(J= 2–1), 13CO(J= 2–1), and C18O(J= 2–1) line emission at a spatial resolution of ∼2 pc. There are two individual molecular clouds with a systematic velocity difference of ∼6 km s−1. Three continuum sources representing up to ∼10 high-mass stars with spectral types of B0V–O7.5V are embedded within the densest parts of molecular clouds bright in the C18O(J= 2–1) line emission. The two molecular clouds show a complementary spatial distribution with a spatial displacement of ∼6.2 pc, and show a V-shaped structure in the position–velocity diagram. These observational features traced by CO and its isotopes are consistent with those in high-mass star-forming regions created by cloud–cloud collisions in the Galactic and Magellanic Cloud H iiregions. Our new finding in M 33 indicates that cloud–cloud collision is a promising process for triggering high-mass star formation in the Local Group.

We present the first X-ray analysis of the diffuse hot ionized gas and the point sources in IC131, after NGC604 the second most X-ray luminous giant H II region (GHR) in M33. The X-ray emission is detected only in the south eastern part of IC131 (named IC131-se) and is limited to an elliptical region of [?]200 pc in extent. This region appears to be confined toward the west by a hemispherical shell of warm ionized gas and only fills about half that volume. Although the corresponding X-ray spectrum has 1215 counts, it cannot conclusively be told whether the extended X-ray emission is thermal, non-thermal, or a combination of both. A thermal plasma model of kTe = 4.3 keV or a single power law of G [?] 2.1 fit the spectrum equally well. If the spectrum is purely thermal (non-thermal), the total unabsorbed X-ray luminosity in the 0.35-8 keV energy band amounts to LX = 6.8(8.7) x 1035 erg s-1. Among other known H II regions IC131-se seems to be extreme regarding the combination of its large extent of the X-ray plasma, the lack of massive O stars, its unusually high electron temperature (if thermal), and the large fraction of LX emitted above 2 keV ([?]40%-53%). A thermal plasma of [?]4 keV poses serious challenges to theoretical models, as it is not clear how high electron temperatures can be produced in H II regions in view of mass-proportional and collisionless heating. If the gas is non-thermal or has non-thermal contributions, synchrotron emission would clearly dominate over inverse Compton emission. It is not clear if the same mechanisms which create non-thermal X-rays or accelerate cosmic rays in supernova remnants can be applied to much larger scales of 200 pc. In both cases the existing theoretical models for GHRs and superbubbles do not explain the hardness and extent of the X-ray emission in IC131-se. We also detect a variable source candidate in IC131. It seems that this object (CXO J013315.10+304453.0) is a high mass X-ray binary whose optical counterpart is a B2-type star with a mass of [?]9 M .

Chandra data of the X-ray source [PMH2004] 47 were obtained in the ACIS Survey of M 33 (ChASeM33) in 2006. During one of the observations, the source varied from a high state to a low state and back, in two other observations it varied from a low state to respectively intermediate states. These transitions are interpreted as eclipse ingresses and egresses of a compact object in a high-mass X-ray binary (HMXB) system. The phase of mideclipse is given by HJD 245 3997.476 +- 0.006, the eclipse half angle is 30.deg6 +- 1.deg2. Adding XMM-Newton observations of [PMH2004] 47 in 2001 we determine the binary period to be 1.732479 +- 0.000027 days. This period is also consistent with ROSAT HRI observations of the source in 1994. No short-term periodicity compatible with a rotation period of the compact object is detected. There are indications for a long-term variability similar to that detected for Her X-1. During the high state the spectrum of the source is hard (power-law spectrum with photon index [?]0.85) with an unabsorbed luminosity of 2 x1037 erg s-1 (0.2-4.5 keV). We identify as an optical counterpart a V [?] 21.0 mag star with T eff>19000 K, log(g)>2.5. The Canada-France-Hawaii Telescope optical light curves for this star show an ellipsoidal variation with the same period as the X-ray light curve. The optical light curve together with the X-ray eclipse can be modeled by a compact object with a mass consistent with a neutron star or a black hole in an HMXB. However, the hard power-law X-ray spectrum favors a neutron star as the compact object in this second eclipsing X-ray binary in M 33. Assuming a neutron star with a canonical mass of 1.4 M and the best-fit companion temperature of 33,000 K, a system inclination i = 72deg and a companion mass of 10.9 M are implied.

NGC 604 is the largest H II region in M33, second only within the Local Group to 30 Dor, and is important as a laboratory for understanding how massive young stellar clusters interact with the surrounding interstellar medium. Here we present deep (300 ks) X-ray imagery of NGC 604 obtained as part of the Chandra ACIS Survey of M33 (ChASeM33), which shows highly structured X-ray emission covering ~70% of the full Ha extent of NGC 604. The main bubbles and cavities in NGC 604 are filled with hot ( kT = 0.5 keV) X-ray-emitting gas, and X-ray spectra extracted from these regions indicate that the gas is thermal. For the western part of NGC 604 we derive an X-ray gas mass of ~4300 M and an unabsorbed (0.35-2.5 keV) X-ray luminosity of LX = 9.3 x 1035 erg s [?]1. These values are consistent with a stellar mass-loss bubble entirely powered by ~200 OB stars. This result is remarkable because the standard bubble model tends to underpredict the luminosity of X-ray-bright bubbles and usually requires additional heating from SNRs. Given a cluster age of ~3 Myr, it is likely that the massive stars have not yet evolved into SNe. We detect two discrete spots of enhanced and harder X-ray emission, which we consider to be fingerprints from a reverse shock produced by a supersonic wind after it collided with the shell wall. In the eastern part of NGC 604 the X-ray gas mass amounts to ~1750 M. However, mass loss from young stars cannot account for the unabsorbed X-ray luminosity of LX = 4.8 x 1035 erg s [?]1. Off-center SNRs could produce the additional luminosity. The bubbles in the east seem to be much older and were most likely formed and powered by young stars and SNe in the past. A similar dichotomy between east and west is seen in the optical, implying that a massive wall of neutral and ionized gas shields the dynamically quiescent east from the actively star-forming west.

The Chandra ACIS Survey of M33 (ChASeM33) has acquired seven fields of ACIS data covering M33 with 200 ks of exposure in each field. A catalog from the first 10 months of data, along with archival Chandra observations dating back to the year 2000, is currently available. We have searched these data for transient sources that are measured to have a 0.35-8.0 keV unabsorbed luminosity of at least 4 x 1035 ergs s[?]1 in one epoch and are not detected in another epoch. This set of the survey data has yielded seven such sources, including one previously known supersoft source. We analyzed XMM-Newton data from the archive distributed over the years 2000-2003 to search for recurrent outbursts and to get a spectrum for the supersoft transient. We find only one recurrent transient in our sample. The X-ray spectra, light curves, and optical counterpart candidates of two of the other sources suggest that they are high-mass X-ray binaries. Archival Spitzer photometry and high X-ray absorption suggest that one of the sources is a highly variable background active galactic nucleus. The other three sources are more difficult to classify. The bright transient population of M33 appears to contain a large fraction of high-mass X-ray binaries compared with the transient populations of M31 and the Galaxy, reflecting the later morphology of M33.

We present and interpret new X-ray data for M33SNR 21, the brightest X-ray supernova remnant (SNR) in M33. The SNR is in seen projection against (and appears to be interacting with) the bright H II region NGC 592. Data for this source were obtained as part of the Chandra ACIS Survey of M33 (ChASeM33) Very Large Project. The nearly on-axis Chandra data resolve the SNR into a ~5'' diameter (20 pc at our assumed M33 distance of 817 +- 58 kpc) slightly elliptical shell. The shell is brighter in the east, which suggests that it is encountering higher density material in that direction. The optical emission is coextensive with the X-ray shell in the north, but extends well beyond the X-ray rim in the southwest. Modeling the X-ray spectrum with an absorbed sedov model yields a shock temperature of 0.46img1.gif keV, with an ionization timescale of net = 2.1img2.gif x 1012 cm-3 s and half-solar abundances (0.45img3.gif). Assuming Sedov dynamics gives an average preshock H density of 1.7 +- 0.3 cm-3. The dynamical age estimate is 6500 +- 600 yr, while the best-fit net value and derived ne gives 8200 +- 1700 yr; the weighted mean of the age estimates is 6700 +- 600 yr. We estimate an X-ray luminosity (0.25-4.5 keV) of (1.2 +- 0.2) x 1037 ergs s-1 (absorbed), and (1.7 +- 0.3) x 1037 ergs s-1 (unabsorbed), in good agreement with the recent XMM-Newton determination. No significant excess hard emission was detected; the luminosity [?]1.2 x 1035 ergs s-1 (2-8 keV) for any hard point source.

Several letters to the editor are presents in response to articles in previous issues including "Sleeping with Your Baby," Peggy O'Mara, "Breakfast Fit for a Queen" and "Give Me that Old-Time Recess."

Suzaku observed the molecular cloud MBM 12 and a blank field less than $3^{\circ}$away to separate the local and distant components of the diffuse soft X-ray background. Towards MBM 12, a local ($D \lesssim 275 \,\mathrm{pc}$) O VII emission line was clearly detected with an intensity of $3.5 \;\mathrm{photons} \;\mathrm{cm}^{-2} \,\mathrm{s}^{-1} \,\mathrm{sr}^{-1}$(or line units, LU), and the O VIII flux was ${<0.34 \;\mathrm{LU}}$. The origin of this O VII emission could be hot gas in the Local Hot Bubble (LHB), charge exchange within the heliosphere with oxygen ions from the solar wind (SWCX), or both. If entirely from the LHB, the emission could be explained by a region with emission measure of $0.0075 \,\mathrm{cm}^{-6} \,\mathrm{pc}$and a temperature of $1.2 \times 10^6 \,\mathrm{K}$. However, this temperature and emission measure implies $1/4 \;\mathrm{keV}$emission in excess of observations. There is no evidence in the X-ray light curve or solar wind data for a significant contribution from geocoronal SWCX, although interplanetary SWCX is still possible. In any case, the observed O VII flux represents an upper limit to both the LHB emission and interplanetary SWCX in this direction. The blank field was observed immediately afterwards. The net off-cloud O VII and O VIII intensities were (respectively) $2.34 \pm 0.33$and $0.77 \pm 0.16 \;\mathrm{LU}$, after subtracting the on-cloud foreground emission. If this more distant O VII and O VIII emission is from a thermal plasma in collisional equilibrium beyond the Galactic disk, we infer it has a temperature of $(2.1 \pm 0.1) \times 10^6 \,\mathrm{K}$with an emission measure of $(4 \pm 0.6) \times 10^{-3} \,\mathrm{cm}^{-6} \,\mathrm{pc}$.

We present Far Ultraviolet Spectroscopic Explorer (FUSE) and X-Ray Multi-Mirror Mission (XMM-Newton) data for the reverse shock of the O-rich supernova remnant (SNR) 1E 0102.2-7219 in the Small Magellanic Cloud (SMC). The FUSE observations cover three regions with significantly different optical [O III] intensities, all associated with the relatively bright part of the X-ray ring. Emission lines of O VI ll1032, 1038 are clearly detected in the FUSE spectra. The XMM-Newton EPIC MOS 1/2 spectra are dominated by strong emission lines of O, Ne, and Mg. By combining the O VI doublet emission with the O VII triplet and O VIII Lya fluxes from the X-ray spectra and assuming a nonequilibrium ionization (NEI) model with a single ionization timescale for the spectra, we find an increase of the ionization timescale t from north (t [?] 0.6 x 1011 s cm-3) to southeast (t [?] 2 x 1011 s cm-3). This is indicative of increasing density in the X-ray-bright ring, in good agreement with the optical [O III] emission, which is strongest in the southeast. However, if we assume a plane-parallel shock model with a distribution of ionization timescales, the O VI emission appears to be inconsistent with O VII and O VIII in X-rays. The analysis of the total X-ray spectra shows that there is no consistent set of values for the temperature and ionization timescale that can explain the observed line ratios for O, Ne, and Mg. This would be consistent with a structured distribution of the ejecta, as the O, Ne, and Mg would have interacted with the reverse shock at different times.

We present evidence for cosmic-ray acceleration at the forward shock in Tycho's supernova remnant (SNR) from three X-ray observables: (1) the proximity of the contact discontinuity to the forward shock, or blast wave, (2) the morphology of the emission from the rim of Tycho, and (3) the spectral nature of the rim emission. We determine the locations of the blast wave (BW), contact discontinuity (CD), and reverse shock (RS) around the rim of Tycho's supernova remnant using a principal component analysis and other methods applied to new Chandra data. The azimuthal-angle-averaged radius of the BW is 251''. For the CD and RS we find average radii of 241'' and 183'', respectively. Taking account of projection effects, we find ratios of 1 : 0.93 : 0.70 (BW : CD : RS). We show these values to be inconsistent with adiabatic hydrodynamic models of SNR evolution. The CD : BW ratio can be explained if cosmic-ray acceleration of ions is occurring at the forward shock. The RS : BW ratio, as well as the strong Fe Ka emission from the Tycho ejecta, imply that the RS is not accelerating cosmic rays. We also extract radial profiles from ~34% of the rim of Tycho and compare them to models of surface brightness profiles behind the BW for a purely thermal plasma with an adiabatic shock. The observed morphology of the rim is much more strongly peaked than predicted by the model, indicating that such thermal emission is implausible here. Spectral analysis also implies that the rim emission is nonthermal in nature, lending further support to the idea that Tycho's forward shock is accelerating cosmic rays.

We present the analysis of the X-ray Multimirror Mission (XMM-Newton) European Photon Imaging Camera (EPIC) data of the Galactic supernova remnant (SNR) CTB 109 (G109.1-1.0). CTB 109 is associated with the anomalous X-ray pulsar (AXP) 1E 2259+586 and has an unusual semicircular morphology in both the X-ray and the radio and an extended X-ray bright interior region known as the "Lobe." The deep EPIC mosaic image of the remnant shows no emission toward the west where a giant molecular cloud complex is located. No morphological connection between the Lobe and the AXP is found. We find remarkably little spectral variation across the remnant given the large intensity variations. All spectra of the shell and the Lobe are well fitted by a single-temperature nonequilibrium ionization model for a collisional plasma with solar abundances [kT [?] 0.5-0.7 keV, t = img1.gif ne dt [?] (1-4) x 1011 s cm-3, NH [?] (5-7) x 1021 cm-2]. There is no indication of nonthermal emission in the Lobe or the shell. We conclude that the Lobe originated from an interaction of the SNR shock wave with an interstellar cloud. Applying the Sedov solution for the undisturbed eastern part of the SNR and assuming full equilibration between the electrons and ions behind the shock front, the SNR shock velocity is derived as vs = 720 +- 60 km s-1, the remnant age as t = (8.8 +- 0.9) x 103d3 yr, the initial energy as E0 = (7.4 +- 2.9) x 1050dimg2.gif ergs, and the preshock density of the nuclei in the ambient medium as n0 = (0.16 +- 0.02)dimg3.gif cm-3, at an assumed distance of D = 3.0d3 kpc. Assuming that CTB 109 and 1E 2259+586 are associated, these values constrain the age and the environment of the progenitor of the SNR and the pulsar.

The newly discovered supernova remnant G266.2-1.2 (RX J0852.0-4622), along the line of sight to the Vela supernova remnant (SNR), was observed with ASCAfor 120 ks. We find that the X-ray spectrum is featureless and well described by a power law, extending to three of the class of shell-type SNRs dominated by nonthermal X-ray emission. Like G347.3-0.5, this low-latitude remnant displays discrete regions of enhanced emission along the rim as well as faint nonthermal emission from the interior. We derive limits on the thermal content of the remnant emission, although the presence of the Vela SNR compromises our ability to seriously constrain a low-temperature component. Limits placed on the amount of Sc-K emission are compared with the expected flux based on the reported 44Ti emission from G266.2-1.2. We also report on an unresolved X-ray source surrounded by diffuse emission near the center of the remnant. The properties of the source are not well determined but appear consistent with the interpretation that the source is a neutron star surrounded by a synchrotron nebula. Alternatively, the source may be associated with one of two stars located within the positional error circle, but this appears somewhat unlikely.

G328.4+0.2 is a moderately small (5' x 5') Galactic radio supernova remnant (SNR) at a distance of at least 17 kpc that has been long suggested to be Crab-like. Here we report on the detection with ASCA of the X-ray emission from the SNR. The X-ray source is faint with an observed flux of (6.0 +- 0.8) x 10-13 ergs s-1 cm-2 over the 2-10 keV band. The emission is heavily cut off at low energies and no flux is detected below 2 keV. Spectral analysis confirms that the column density to the source is indeed large, NH ~ 1023 atoms cm-2, and consistent with the total column density of hydrogen through the Galaxy at this position. Good fits to the spectrum can be obtained for either thermal plasma or nonthermal power-law models, although the lack of detected line emission as well as other evidence argues against the former interpretation. The power-law index we find, aP = 2.9img1.gif, is consistent with other Crab-like SNRs. In the radio band, G328.4+0.2 is nearly as luminous as the Crab Nebula, yet in the X-ray band, it is some 70 times fainter. Nevertheless, its inferred soft X-ray band luminosity is greater than all but the brightest pulsar-powered synchrotron nebulae and implies that G328.4+0.2 contains a rapidly spinning, as yet undetected, pulsar that is losing energy at a rate of ~1038 ergs s-1.

Caveolin-1 is an integral membrane protein that is the primary component of cell membrane invaginations called caveolae. While caveolin-1 is known to participate in a myriad of vital cellular processes, structural data on caveolin-1 of any kind is severely limited. In order to rectify this dearth, secondary structure analysis of a functional construct of caveolin-1, containing the intact C-terminal domain, was performed using NMR spectroscopy in lyso-myristoylphosphatidylglycerol micelles. Complete backbone assignments of caveolin-1 (residues 62–178) were made, and it was determined that residues 62–79 were dynamic; residues 89–107, 111–128, and 132–175 were helical; and residues 80–88, 108–110, and 129–131 represent unstructured breaks between the helices.

Recent ASCA observations of G347.3-0.5, a supernova remnant (SNR) discovered in the ROSAT All-Sky Survey, reveal nonthermal emission from a region along the northwestern shell. Here we report on new pointed ASCA observations of G347.3-0.5 that confirm this result for all the bright shell regions and also reveal similar emission, although with slightly different spectral properties, from the remainder of the SNR. Curiously, no thermal X-ray emission is detected anywhere in the remnant. We derive limits on the amount of thermal emitting material present in G347.3-0.5 and present new radio continuum, CO, and infrared results that indicate that the remnant is distant and of moderate age. We show that our observations are broadly consistent with a scenario that has most of the supernova remnant shock wave still within the stellar wind bubble of its progenitor star, while part of it appears to be interacting with denser material. A point source at the center of the remnant has spectral properties similar to those expected for a neutron star and may represent the compact relic of the supernova progenitor.

In this paper we present a new look at the distribution of emission responsible for the soft X-ray diffuse background (SXRB) using ROSATall-sky survey data. This is prompted by the demonstration of the existence of extensive 1/4 keV emission in the Galactic halo that was not considered in the most successful previous model, in which the bulk of the observed 1/4 keV X-rays originated in a Local Hot Bubble (LHB) that surrounds the Sun. The basic distribution can be represented by two angularly varying Galactic components (the LHB and an X-ray halo) and an isotropic extragalactic component. In addition, there are the distinct enhancements of supernova remnants, superbubbles, and clusters of galaxies.

We present the first analysis of an XMM-Newton observation of the nearby molecular cloud MBM 12. We find that in the direction of MBM 12 the total O VII (0.57 keV) triplet emission is 1.8+0.5 -0.6 photons cm-2 s-1 sr-1 (or line units, LU) while for the O VIII (0.65 keV) line emission we find a 3s upper limit of <1 LU. We use a heliospheric model to calculate the O VII and O VIII emission generated by Solar Wind Charge-eXchange (SWCX) which we compare to the XMM-Newton observations. This comparison provides new constraints on the relative heliospheric and Local Bubble contributions to the local diffuse X-ray background. The heliospheric SWCX model predicts 0.82 LU for O VII, which accounts for [?]46% +- 15% of the observed value, and 0.33 LU for the O VIII line emission consistent with the XMM-Newton observed value. We discuss our results in combination with previous observations of MBM 12 with Chandra and Suzaku.

Context.For many years, X-ray astronomy missions have used the Crab nebula as a celestial calibration source for the X-ray flux and spectral shape. However, the object is often too bright for current and future missions equipped with instruments with improved sensitivity.