Phase-resolved Hubble Space Telescope ultraviolet spectroscopy

We present highly time-resolved HST FOS UV spectroscopy of the nova-like binary V795 Her. Several key results emerge. For the first time we find a strong 2.6-h signature in the variability of the UV lines. The HST data reveal no evidence of a 4.8-h ‘period’, in contrast to our previous IUE observations. This, and differences in the spectral line characteristics, suggests that HST found the system in a different state from earlier IUE observations. The C IV line alone contains a fairly stable, asymmetric, extended blueward absorption trough which we associate with a wind outflow. The 2.6-h variations of the line profiles are largely confined to an interval of about 0.4 in phase and to the velocity regime −1500 < v < 0 km s−1, the changes being dominated by the apparent decline and re-emergence of a blueshifted emission peak. The complex profiles permit many empirical interpretations, but the simplest attributes the variability to a narrow (FWHM∼1000 km s−1) emission component which is always blueshifted with a mean velocity of around –600 km s−1. This interpretation, however, is not readily related to any obvious source within the binary. An alternative picture, which attempts to relate the UV and (simultaneously observed) optical line behaviour, invokes a more stable, broad (FWHM∼2000 km s−1) emission feature, the intrinsic morphology of which is disguised by superposed constant and variable absorption components. One tentative physical explanation of such a decomposition involves an accretion stream that overflows the accretion disc. However, several problems with this model remain to be resolved. We also draw attention to similarities between the velocity-restricted behaviour in the UV lines of V795 Her and that in the optical lines of T Tauri stars. This might indicate a connection between V795 Her and the magnetically influenced inflow/outflow characteristics associated with the central star in T Tauri systems. If such a connection were eventually demonstrated, it would reopen the question of whether the 2.6-h period in V795 Her is really the binary period and whether the system is in fact related to the intermediate polars

Excited hydrogen and the formation of molecular hydrogen via associative ionization – I. Physical processes and outflows from young stellar objects

Rates for the associative ionization reaction H(n=2)+H→H+2+e− are calculated. This reaction is found to be a greater contributor to the H2 formation rate than the direct radiative association reaction H(n=2)+H→H2+hν in most regions of astrophysical interest. Chemical models of circumstellar regions are reassessed in the light of this information. We also examine the chemical behaviour of several other excited chemical species. A critical examination reveals that excitation effects are, in general, very important in many astrophysical situations and must be incorporated into the chemistry. H2 has been detected in a variety of circumstellar regions and has a pivotal role in the overall chemistry. The method and efficiency of its formation are therefore of great importance. We test the significance of the associative ionization reaction in several models. These models include a schematic description of the radiative transfer in H I Lyα. The endothermicity (≃ 1.1 eV) of the reaction and the high departures from LTE that are required for the H I (n = 2) level to be sufficiently populated restrict its significance to regions of high excitation, such as are found in circumstellar regions. In this paper (I), we investigate the importance of the reaction in winds associated with young stellar objects. In Paper II, the investigation will be extended to include novae, supernovae, planetary nebulae and shocked regions. The results indicate that reactions involving excited atomic states may be very important in a number of circumstellar chemistries. Only exceptionally will reactions involving the higher excited states (n > 2) be as significant as those involving H(n = 2)

Astrophysically important reactions involving excited hydrogen

The associative ionization reaction H(n=2) + H → H+2 + e− is found to be a greater contributor to the H2 formation rate than the direct radiative association reaction H(n=2) + H → H2 + hν in most regions of astrophysical interest. The endothermicity (≂1.1 eV) of the reaction and the high departures from LTE that are required for the H I (n=2) level to be sufficiently populated restrict its significance to regions of high excitation. The reaction H(n=2) + H+ → H+2 + hν may be significant in highly excited ionized regions, such as planetary nebulae and shocks. Chemical models of circumstellar regions have been reassessed in the light of this information. A critical examination reveals tht excitation effects are, in general, very important in many astrophysical situations. Only exceptionally, will reactions involving the higher excited states (n≳2) be as significant as those involving H(n=2)

A NITROGEN-ENRICHED NEBULA AROUND P-CYGNI

We have detected extended nebular emission in [S II]λλ6716,6731, [N II] λ6584,6584andHα on a long-slit spectrum offset by 9 arcsec from P Cyg. Anomalously strong [Ni II]λ6666.8 emission was also detected. The [S II] doublet ratio yields an electron density of 600 cm–3. The [N II] and [S II] lines have been used to derive an N/S ratio which is insensitive to the adopted value of electron temperature. The N/S ratio is 33 ± 5 by number, five times higher than solar, implying that the material has undergone CN-cycle processing which has converted most of the original carbon into nitrogen

Chandra observations of Cygnus OB2

Cygnus OB2 is the nearest example of a massive star forming region, containing over 50 O-type stars and hundreds of B-type stars. We have analyzed two Chandra pointings in Cyg OB2, detecting ~1700 X-ray sources, of which ~1450 are thought to be members of the association. Optical and near-IR photometry has been obtained for ~90% of these sources from recent deep Galactic plane surveys. We have performed isochrone fits to the near-IR color-magnitude diagram, deriving ages of 3.5(+0.75,-1.0) and 5.25(+1.5,-1.0) Myrs for sources in the two fields, both with considerable spreads around the pre-MS isochrones. The presence of a second population in the region, somewhat older than the present-day O-type stars, has been suggested by other authors and fits with the ages derived here. The fraction of sources with inner circumstellar disks (as traced by the K-band excess) is found to be very low, but appropriate for a population of age ~5 Myrs. We measure the stellar mass functions and find a power-law slope of Gamma = -1.09 +/- 0.13, in good agreement with the global mean value estimated by Kroupa. A steepening of the mass function at high masses is observed and we suggest this is due to the presence of the previous generation of stars that have lost their most massive members. Finally, combining our mass function and an estimate of the radial density profile of the association suggests a total mass of Cyg OB2 of ~30,000 Msun, similar to that of many of our Galaxy's most massive star forming regions.Comment: 6 pages, 4 figures, conference proceedings for JENAM 2010: Star Clusters in the Era of Large Surveys, Editors: A.Moitinho and J. Alve

Galactic AGB stars from the IPHAS survey

We present a photometric analysis of the properties of asymptotic giant branch stars identified in the INT Photometric H-alpha Survey (IPHAS) of the northern Galactic plane. Follow-up spectroscopy has revealed that the IPHAS (r - Ha) colour is a valuable diagnostic of the photospheric C/O ratio, and may be used to identify hundreds of carbon and S-type stars

High-threshold mechanosensitive ion channels blocked by a novel conopeptide mediate pressure-evoked pain

Little is known about the molecular basis of somatosensory mechanotransduction in mammals. We screened a library of peptide toxins for effects on mechanically activated currents in cultured dorsal root ganglion neurons. One conopeptide analogue, termed NMB-1 for noxious mechanosensation blocker 1, selectively inhibits (IC50 1 µM) sustained mechanically activated currents in a subset of sensory neurons. Biotinylated NMB-1 retains activity and binds selectively to peripherin-positive nociceptive sensory neurons. The selectivity of NMB-1 was confirmed by the fact that it has no inhibitory effects on voltage-gated sodium and calcium channels, or ligand-gated channels such as acid-sensing ion channels or TRPA1 channels. Conversely, the tarantula toxin, GsMTx-4, which inhibits stretch-activated ion channels, had no effects on mechanically activated currents in sensory neurons. In behavioral assays, NMB-1 inhibits responses only to high intensity, painful mechanical stimulation and has no effects on low intensity mechanical stimulation or thermosensation. Unexpectedly, NMB-1 was found to also be an inhibitor of rapid FM1-43 loading (a measure of mechanotransduction) in cochlear hair cells. These data demonstrate that pharmacologically distinct channels respond to distinct types of mechanical stimuli and suggest that mechanically activated sustained currents underlie noxious mechanosensation. NMB-1 thus provides a novel diagnostic tool for the molecular definition of channels involved in hearing and pressure-evoked pain

The O star hinterland of the Galactic starburst, NGC 3603

The very bright and compact massive young cluster, NGC 3603, has been cited as an example of a starburst in the Milky Way and compared with the much-studied R136/30 Doradus region in the Large Magellanic Cloud. Here we build on the discovery by Mohr-Smith et al. (2017) of a large number of reddened O stars around this cluster. We construct a list of 288 candidate O stars with proper motions, in a region of sky spanning 1.5 × 1.5 square degrees centered on NGC 3603, by cross-matching the Mohr-Smith et al. (2017) catalogue with Gaia DR2 (Gaia Collaboration et al. 2018). This provides the basis for a first comprehensive examination of the proper motions of these massive stars in the halo of NGC 3603, relative to the much better studied central region. We identify up to 11 likely O star ejections – 8 of which would have been ejected between 0.60 and 0.95 Myr ago (supporting the age of ∼1 Myr that has been attributed to the bright cluster centre). Seven candidate ejections are arranged in a partial ring to the south of the cluster core spanning radii of 9–18 arcmin (18–36 pc if the cluster is 7 kpc away). We also show that the cluster has a halo of a further ∼100 O stars extending to a radius of at least 5 arcmin, adding to the picture of NGC 3603 as a scaled down version of the R136/30 Dor region

Proper motions of OB stars in the far Carina Arm

ABSTRACT In large-scale maps of the Galactic disc, the Carina Arm stands out as a clear spiral feature, hosting prominent star clusters and associations rich in massive stars. We study the proper motions of 4199 O and early B most likely in the far Carina Arm, at distances mainly in excess of 4 kpc from the Sun, within the sky region, 282° &amp;lt; ℓ &amp;lt; 294° and −3° &amp;lt; b &amp;lt; +1° (Galactic coordinates). The sample is constructed by extending an existing blue-selected catalogue, and cross-matching with Gaia EDR3 astrometry. The observed pattern of proper motions is modulated into a saw-tooth pattern, with full amplitude approaching 1 mas yr−1, recurring roughly every 2–3 degrees of longitude (200–300 pc at the median OB-star distance of 5.8 kpc). Kinematic perturbation of underlying circular rotation is most likely present. The data also reveal a moving group containing &amp;gt;50 OB stars at ℓ ∼ 286°, b ∼ −1.4° behind the main run of the far arm. An analysis of relative proper motions is performed that yields an incidence of runaway O stars of at least 10 per cent (potentially &amp;gt;20 per cent when full space motions become available). To map where runaways have run away from, we set up simulations for the region that assume linear trajectories and test for trajectory impact parameter in order to identify likely ejection hot spots. We find the method currently gives good results for times of flight of up to ∼4 Myr. It shows convincingly that only NGC 3603 and Westerlund 2 have ejected OB stars in significant numbers. Indeed, both clusters have experienced intense spells of ejection between 0.6–0.9 and 0.5–0.8 Myr ago, respectively.</jats:p

Spectroscopic follow-up of a subset of the Gaia/IPHAS catalogue of Hα-excess sources

State-of-the-art techniques to identify Hα emission-line sources in narrow-band photometric surveys consist of searching for  Hα excess with reference to nearby objects in the sky (position-based selection). However, while this approach usually yields very few spurious detections, it may fail to select intrinsically faint and/or rare Hα-excess sources. In order to obtain a more complete representation of the heterogeneous emission-line populations, we recently developed a technique to find outliers relative to nearby objects in the colour–magnitude diagram (CMD-based selection). By combining position-based and CMD-based selections, we built an updated catalogue of Hα-excess candidates in the Northern Galactic Plane. Here, we present spectroscopic follow-up observations and classification of 114 objects from this catalogue that enables us to test our novel selection method. Out of the 70 spectroscopically confirmed Hα-emitters in our sample, 15 were identified only by the CMD-based selection, and would have been thus missed by the classic position-based technique. In addition, we explore the distribution of our spectroscopically confirmed emitters in the Gaia CMD. This information can support the classification of emission-line sources in large surveys such as the upcoming WEAVE and 4-m Multi-Object Spectroscopic Telescope, especially if augmented with the introduction of other colours