Abstract
We present an extinction map of the inner ∼15′ by 16′ of the Galactic center (GC) with map pixels measuring 5″ × 5″ using integrated light color measurements in the near- and mid-infrared. ...We use a variant of the Rayleigh–Jeans color excess (RJCE) method first described by Majewski et al. as the basis of our work, although we have approached our problem with a Bayesian mindset and dispensed with point-source photometry in favor of surface photometry, turning the challenge of the extremely crowded field at the GC into an advantage. Our results show that extinction at the GC is not inconsistent with a single power-law coefficient,
β
= 2.03 ± 0.06, and compare our results with those using the red clump (RC) point-source photometry method of extinction estimation. We find that our measurement of
β
and its apparent lack of spatial variation are in agreement with prior studies, despite the bimodal distribution of values in our extinction map at the GC with peaks at 5 and 7.5 mag. This bimodal nature of extinction is likely due to the infrared dark clouds that obscure portions of the inner GC field. We present our extinction law and map of the GC region using the point-source catalog of infrared sources compiled by DeWitt et al. The dereddening is limited by the error in the extinction measurement (typically 0.6 mag), which is affected by the size of our map pixels and is not fine-grained enough to separate out the multiple stellar populations present toward the GC.
We analyzed multiwavelength observations of the previously identified Galactic center X-ray binary CXO 174528.79-290942.8 (XID 6592) and determine that the near-infrared counterpart is a red ...supergiant based on its spectrum and luminosity. Scutum X-1 is the only previously known X-ray binary with a red supergiant donor star and closely resembles XID 6592 in terms of X-ray luminosity (LX), absolute magnitude, and IR variability (LIR,var), supporting the conclusion that XID 6592 contains a red supergiant donor star. The XID 6592 infrared counterpart shows variability of ∼0.5 mag in the Wide-field Infrared Survey Explorer-1 band (3.4 m) on timescales of a few hours. Other infrared data sets also show large-amplitude variability from this source at earlier epochs but do not show significant variability in recent data. We do not expect red supergiants to vary by ∼50% in luminosity over these short timescales, indicating that the variability should be powered by the compact object. However, the X-ray luminosity of this system is typically ∼1000× less than the variable luminosity in the infrared and falls below the Chandra detection limit. While X-ray reprocessing can produce large-amplitude fast infrared variability, it typically requires LIR,var to do so, indicating that another process must be at work. We suggest that this system may be a supergiant fast X-ray transient (SFXT), and that a large (∼1038 ergs s−1), fast (102-4 s) X-ray flare could explain the rapid IR variability and lack of a long-lasting X-ray outburst detection. SFXTs are normally associated with blue supergiant companions, so if confirmed, XID 6592 would be the first red supergiant SFXT, as well as the second X-ray red supergiant binary.
We present a method for characterizing image-subtracted objects based on shapelet analysis to identify transient events in ground-based time-domain surveys. We decompose the image-subtracted objects ...onto a set of discrete Zernike polynomials and use their resulting coefficients to compare them to other point-like objects. We derive a norm in this Zernike space that we use to score transients for their point-like nature and show that it is a powerful comparator for distinguishing image artifacts, or residuals, from true astrophysical transients. Our method allows for a fast and automated way of scanning overcrowded, wide-field telescope images with minimal human interaction and we reduce the large set of unresolved artifacts left unidentified in subtracted observational images. We evaluate the performance of our method using archival intermediate Palomar Transient Factory and Dark Energy Camera survey images. However, our technique allows flexible implementation for a variety of different instruments and data sets. This technique shows a reduction in image subtraction artifacts by 99.95% for surveys extending up to hundreds of square degrees and has strong potential for automated transient identification in electromagnetic follow-up programs triggered by the Laser Interferometer Gravitational Wave Observatory-Virgo Scientific Collaboration.
ABSTRACT
This paper provides a catalogue of stars, quasars, and galaxies for the Southern Photometric Local Universe Survey Data Release 2 (S-PLUS DR2) in the Stripe 82 region. We show that a 12-band ...filter system (5 Sloan-like and 7 narrow bands) allows better performance for object classification than the usual analysis based solely on broad bands (regardless of infrared information). Moreover, we show that our classification is robust against missing values. Using spectroscopically confirmed sources retrieved from the Sloan Digital Sky Survey DR16 and DR14Q, we train a random forest classifier with the 12 S-PLUS magnitudes + 4 morphological features. A second random forest classifier is trained with the addition of the W1 (3.4 $\mu\mathrm{m} $) and W2 (4.6 $\mu\mathrm{m} $) magnitudes from the Wide-field Infrared Survey Explorer (WISE). Forty-four per cent of our catalogue have WISE counterparts and are provided with classification from both models. We achieve 95.76 per cent (52.47 per cent) of quasar purity, 95.88 per cent (92.24 per cent) of quasar completeness, 99.44 per cent (98.17 per cent) of star purity, 98.22 per cent (78.56 per cent) of star completeness, 98.04 per cent (81.39 per cent) of galaxy purity, and 98.8 per cent (85.37 per cent) of galaxy completeness for the first (second) classifier, for which the metrics were calculated on objects with (without) WISE counterpart. A total of 2926 787 objects that are not in our spectroscopic sample were labelled, obtaining 335 956 quasars, 1347 340 stars, and 1243 391 galaxies. From those, 7.4 per cent, 76.0 per cent, and 58.4 per cent were classified with probabilities above 80 per cent. The catalogue with classification and probabilities for Stripe 82 S-PLUS DR2 is available for download.
Soft contact lenses are medical devices made from aqueous polymeric gels that are worn on the eye to correct refractive errors. These devices interrupt the natural contact pairing between the cornea ...and the eyelid and create two interfaces comprised of a synthetic material and the epithelia—contact lens surfaces versus (1) the cornea and (2) the eyelid conjunctiva. The cellular responses to friction and shear stress are thought to contribute to contact lens discomfort. This study performs direct contact shear experiments using in vitro biotribological experiments using a microtribometer equipped with a hydrogel membrane probe. Sections from commercial contact lenses are held in place on a spherically capped membrane probe during reciprocating sliding experiments against confluent monolayers of living human telomerase-immortalized corneal epithelial cells (hTCEpi). The contact lenses were loaded against the cell monolayers to physiological contact pressures between 400 and 1300 Pa under an applied load of 200 µN. The reciprocating distance was 3 mm, at a sliding speed of 1 mm/s, and the maximum duration of sliding was 1000 cycles. Five commercially available lenses (somofilcon A, stenfilcon A, etafilcon A, verofilcon A, and delefilcon A) were used to evaluate the cell layer responses to aqueous gels of differing composition, surface modulus, and lubricity. Cell damage was measured via propidium iodide staining and in situ fluorescence microscopy. The shear stresses varied from 16 ± 2 Pa (delefilcon A and verofilcon A) to 86 ± 12 Pa (stenfilcon A), and cell damage increased with increasing shear stress and increasing sliding duration. The two lens materials that have high water content surface gel layers (delefilcon A and verofilcon A) showed distinctly lower measures of cell damage as compared to the other lenses. Surface gel layers with a large polymer mesh size and high water content are shown to be an effective approach to lower the contact pressure, lower the friction coefficient, and thereby lower the shear stress and cell damage.
The new technique of speckle stabilization has great potential to provide optical imaging data at the highest angular resolutions from the ground. While speckle stabilization was initially conceived ...for integral field spectroscopic analyses, the technique shares many similarities with speckle imaging (specifically, shift-and-add and lucky imaging). Therefore, it is worth comparing the two for imaging applications. We have modeled observations on a 2.5 m class telescope to assess the strengths and weaknesses of the two techniques. While the differences are relatively minor, we find that speckle stabilization is a viable competitor to current lucky imaging systems. Specifically, we find that speckle stabilization is 3.35 times more efficient (where efficiency is defined as signal-to-noise ratio S/N per observing interval) than shift-and-add and is able to detect targets 1.42 mag fainter when using a standard system. If we employ a high-speed shutter to compare with lucky imaging at 1% image selection, speckle stabilization is 1.28 times more efficient and 0.31 mag more sensitive. However, when we incorporate potential modifications to lucky imaging systems, we find that the advantages are significantly mitigated—and even reversed—in the 1% frame-selection cases. In particular, we find that in the limiting case of optimal lucky imaging, that is, zero read noiseandphoton counting, we find lucky imaging is 1.80 times more efficient and 0.96 mag more sensitive than speckle stabilization. For the cases in between, we find that there is a gradation in advantages to the different techniques, depending on target magnitude, fraction of frames used, and system modifications. Overall, however, we find that the real strength of lucky imaging is in observations of the brightest targets at all frame-selection levels and in observations of faint targets at the 1% level. For targets in the middle, we find that speckle stabilization regularly achieves higher S/N.
We present the results of wide integral-field near-infrared (1.0-1.8 mum) spectroscopic observations of the southeastern shell of the young core-collapse supernova remnant (SNR) G11.2-0.3. We first ...construct FeII 1.644 mum line images of three bright clumps from the obtained spectral image cubes and compare them with those of other transitions such as FeII 1.257, FeII 1.534, and He I 1.083 mum line images. This allows us to estimate the electron density (~4700-9400 cur super(-3)) and extinction (A sub(V) ~ 16-20 mag) of the shell, including a detailed two-dimensional distribution of the properties in the brightest clump, as well as the discovery of a faint high-velocity (~-440 km s super(-1)) component in the clump. Our SNR shock model calculations estimate the pre-shock number density of ~250-500 cm super(-3) and shock speed of ~80-250 km s super(-1) in the FeII-emitting region of the SNR. The comparison between the observed and modeled radial profiles of the line intensities and their ratios reveals that the shell is composed of multiple thin filaments which have been likely formed in episodic mass-loss processes of a progenitor star. The discovery of the faint high-velocity component supports the interpretation that the southeastern shell of G11.2-0.3 is mainly composed of circumstellar material with contamination by supernova ejecta and also that its ejected material was expelled primarily in the southeast-northwest direction.
The Apache Point Observatory Galactic Evolution Experiment (APOGEE)-one of the Sloan Digital Sky Survey III programs-is using near-infrared (NIR) spectra of ~ 100,000 red giant branch star candidates ...to study the structure of the Milky Way. In the course of the survey, APOGEE also acquires spectra of hot field stars to serve as telluric calibrators for the primary science targets. We report the serendipitous discovery of two rare, fast-rotating B-stars of the sigma Ori E type among those blue field stars observed during the first year of APOGEE operations. Both of the discovered stars display the spectroscopic signatures of rigidly rotating magnetospheres (RRM) common to this class of highly magnetized (B ~ 10 kGauss) stars, increasing the number of known RRM stars by ~10%. One (HD 345439) is a main-sequence B-star with unusually strong He absorption (similar to sigma Ori E), while the other (HD 23478) fits a "He-normal" B3IV classification. We combine the APOGEE discovery spectra with other optical and NIR spectra of these two stars, and of sigma Ori E itself, to show how NIR spectroscopy can be a uniquely powerful tool for discovering more of these rare objects, which may show little/no RRM signatures in their optical spectra. We discuss the potential for further discovery of sigma Ori E type stars, as well as the implications of our discoveries for the population of these objects and insights into their origin and evolution.
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