The Siricidae (Hymenoptera: Symphyta) of Florida

The six species of Siricidae (Hymenoptera: Symphyta) occurring in Florida and one species of regulatory concern introduced to North America are reviewed. Included are diagnoses of Eriotremex formosanus (Matsumura), Sirex areolatus (Cresson), Sirex nigricornis Fabricius, Tremex columba (Linnaeus), Urocerus cressoni Norton, Urocerus taxodii (Ashmead) and Sirex noctilio (Fabricius). A key to species, photographs of morphological features, biological notes and distribution data are provided. For the species T. columba, S. nigricornis, U. taxodii, and U. cressoni, a total of eight new state records are presented

Probing the Interstellar Dust towards the Galactic Centre: Dust Scattering Halo around AX J1745.6-2901

AX J1745.6-2901 is an X-ray binary located at only 1.45 arcmin from Sgr A*, showcasing a strong X-ray dust scattering halo. We combine Chandra and XMM-Newton observations to study the halo around this X-ray binary. Our study shows two major thick dust layers along the line of sight (LOS) towards AX J1745.6-2901. The LOS position and $N_{H}$ of these two layers depend on the dust grain models with different grain size distribution and abundances. But for all the 19 dust grain models considered, dust Layer-1 is consistently found to be within a fractional distance of 0.11 (mean value: 0.05) to AX J1745.6-2901 and contains only (19-34)% (mean value: 26%) of the total LOS dust. The remaining dust is contained in Layer-2, which is distributed from the Earth up to a mean fractional distance of 0.64. A significant separation between the two layers is found for all the dust grain models, with a mean fractional distance of 0.31. Besides, an extended wing component is discovered in the halo, which implies a higher fraction of dust grains with typical sizes $\lesssim$ 590 \AA\ than considered in current dust grain models. Assuming AX J1745.6-2901 is 8 kpc away, dust Layer-2 would be located in the Galactic disk several kpc away from the Galactic Centre (GC). The dust scattering halo biases the observed spectrum of AX J1745.6-2901 severely in both spectral shape and flux, and also introduces a strong dependence on the size of the instrumental point spread function and the source extraction region. We build Xspec models to account for this spectral bias, which allow us to recover the intrinsic spectrum of AX J1745.6-2901 free from dust scattering opacity. If dust Layer-2 also intervenes along the LOS to Sgr A* and other nearby GC sources, a significant spectral correction for the dust scattering opacity would be necessary for all these GC sources.Comment: 20 pages, published by MNRAS; revised values in Table-1 and Table-B

The Impact of Accurate Extinction Measurements for X-ray Spectral Models

Interstellar extinction includes both absorption and scattering of photons from interstellar gas and dust grains, and it has the effect of altering a source's spectrum and its total observed intensity. However, while multiple absorption models exist, there are no useful scattering models in standard X-ray spectrum fitting tools, such as XSPEC. Nonetheless, X-ray halos, created by scattering from dust grains, are detected around even moderately absorbed sources and the impact on an observed source spectrum can be significant, if modest, compared to direct absorption. By convolving the scattering cross section with dust models, we have created a spectral model as a function of energy, type of dust, and extraction region that can be used with models of direct absorption. This will ensure the extinction model is consistent and enable direct connections to be made between a source's X-ray spectral fits and its UV/optical extinction.Comment: 8 pages, 4 figure

Black Holes and Vacuum Cleaners: Using Metaphor, Relevance, and Inquiry in Labels for Space Images

This study extended research on the development of explanatory labels for astronomical images for the non-expert lay public. The research questions addressed how labels with leading questions/metaphors and relevance to everyday life affect comprehension of the intended message for deep space images, the desire to learn more, and the aesthetic appreciation of images. Participants were a convenience sample of 1,921 respondents solicited from a variety of websites and through social media who completed an online survey that used four high-resolution images as stimuli: Sagittarius A*, Solar Flare, Cassiopeia A, and the Pinwheel Galaxy (M101). Participants were randomly assigned initially to 1 of 3 label conditions: the standard label originally written for the image, a label with a leading question containing a metaphor related to the information for the image, or a label that contained a fact about the image relevant to everyday life. Participants were randomly assigned to 1 image and compared all labels for that image. Open-ended items at various points asked participants to pose questions to a hypothetical astronomer. Main findings were that the relevance condition was significantly more likely to increase wanting to learn more; the original label was most likely to increase overall appreciation; and, smart phone users were more likely to want to learn more and report increased levels of appreciation. Results are discussed in terms of the need to examine individual viewer characteristics and goals in creating different labels for different audiences.Comment: 50 pages, 7 tables, 2 figures, accepted by the journal "Psychology of Aesthetics, Creativity, and the Arts

The Chandra X-ray Observatory: An Astronomical Facility Available to the World

The Chandra X-ray observatory, one of NASA's "Great Observatories," provides high angular and spectral resolution X-ray data which is freely available to all. In this review I describe the instruments on chandra along with their current calibration, as well as the chandra proposal system, the freely-available Chandra analysis software package CIAO, and the Chandra archive. As Chandra is in its 6th year of operation, the archive already contains calibrated observations of a large range of X-ray sources. The Chandra X-ray Center is committed to assisting astronomers from any country who wish to use data from the archive or propose for observation

Effects of Interstellar Dust Scattering on the X-ray Eclipses of the LMXB AX J1745.6-2901 in the Galactic Center

AX J1745.6-2901 is an eclipsing low mass X-ray binary (LMXB) in the Galactic Centre (GC). It shows significant X-ray excess emission during the eclipse phase, and its eclipse light curve shows an asymmetric shape. We use archival XMM-Newton and Chandra observations to study the origin of these peculiar X-ray eclipsing phenomena. We find that the shape of the observed X-ray eclipse light curves depends on both photon energy and the shape of the source extraction region, and also shows differences between the two instruments. By performing detailed simulations for the time-dependent X-ray dust scattering halo, as well as directly modelling the observed eclipse and non-eclipse halo profiles of AX J1745.6-2901, we obtained solid evidence that its peculiar eclipse phenomena are indeed caused by the X-ray dust scattering in multiple foreground dust layers along the line-of-sight (LOS). The apparent dependence on the instruments is caused by different instrumental point-spread-functions. Our results can be used to assess the influence of dust scattering in other eclipsing X-ray sources, and raise the importance of considering the timing effects of dust scattering halo when studying the variability of other X-ray sources in the GC, such as Sgr A*. Moreover, our study of halo eclipse reinforces the existence of a dust layer local to AX J1745.6-2901 as reported by Jin et al. (2017), as well as identifying another dust layer within a few hundred parsecs to Earth, containing up to several tens of percent LOS dust, which is likely to be associated with the molecular clouds in the Solar neighbourhood. The remaining LOS dust is likely to be associated with the molecular clouds located in the Galactic disk in-between.Comment: 25 pages, 18 figures, 5 tables, accepted by MNRA