Stellar occultations-the passing of a relatively nearby body in front of a background star-can be used to probe the atmosphere of the closer body with a spatial resolution of a few kilometres (ref. ...1). Such observations can yield the scale height, temperature profile, and other information about the structure of the occulting atmosphere. Occultation data acquired for Pluto's atmosphere in 1988 revealed a nearly isothermal atmosphere above a radius of ∼1,215 km. Below this level, the data could be interpreted as indicating either an extinction layer or the onset of a large thermal gradient, calling into question the fundamental structure of this atmosphere. Another question is to what extent Pluto's atmosphere might be collapsing as it recedes from the Sun (passing perihelion in 1989 in its 248-year orbital period), owing to the extreme sensitivity of the equilibrium surface pressure to the surface temperature. Here we report observations at a variety of visible and infrared wavelengths of an occultation of a star by Pluto in August 2002. These data reveal evidence for extinction in Pluto's atmosphere and show that it has indeed changed, having expanded rather than collapsed, since 1988.
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DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
We present near-IR JH spectra of the central regions of the dwarf starburst galaxy NGC 1569 using the Florida Image Slicer for Infrared Cosmology and Astrophysics (FISICA). The dust-penetrating ...properties and available spectral features of the near-IR, combined with the integral field unit (IFU) capability to take spectra of a field, make FISICA an ideal tool for this work. We use the prominent He i (1.083 μm) and Paβ (1.282 μm) lines to probe the dense star-forming regions as well as characterize the general star-forming environment around the super star clusters (SSCs) in NGC 1569. We find He i coincident with CO clouds to the north and west of the SSCs, which provides the first, conclusive evidence for embedded star clusters here.
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.
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.
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.
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We present a machine learning methodology to separate quasars from galaxies and stars using data from S-PLUS in the Stripe-82 region. In terms of quasar classification, we achieved 95.49% for ...precision and 95.26% for recall using a Random Forest algorithm. For photometric redshift estimation, we obtained a precision of 6% using k-Nearest Neighbour.
We report near-infrared photometry, spectroscopy, and speckle imaging of the hot, luminous star we identify as candidate LBV 1806-20. We also present photometry and spectroscopy of three nearby ...stars, which are members of the same star cluster containing LBV 1806-20 and SGR 1806-20. The spectroscopy and photometry show that LBV 1806-20 is similar in many respects to the luminous "Pistol star," albeit with some important differences. They also provide estimates of the effective temperature and reddening of LBV 1806-20 and confirm distance estimates, leading to a best estimate for the luminosity of this star of greater than 5 x 10 super(6) L sub( ). The nearby cluster stars have spectral types and inferred absolute magnitudes that confirm the distance (and thus luminosity) estimate for LBV 1806-20. If we drop kinematic measurements of the distance (15.1 super(+) sub(-) super(1) sub(1) super(.) sub(.) super(8) sub(3) kpc), we have a lower limit on the distance of greater than 9.5 kpc and on the luminosity of greater than 2 x 10 super(6) L sub( ), based on the cluster stars. If we drop both the kinematic and cluster star indicators for distance, an ammonia absorption feature sets yet another lower limit to the distance of greater than 5.7 kpc, with a corresponding luminosity estimate of greater than 7 x 10 super(5) L sub( )for the candidate LBV 1806-20. Furthermore, on the absis of very high angular resolution speckle images, we determine that LBV 1806-20 is not a cluster of stars but is rather a single star or binary system. Simple arguments based on the Eddington luminosity lead to an estimate of the total mass of LBV 1806-20 (single or binary) exceeding 190 M sub( ). We discuss the possible uncertainties in these results and their implications for the star formation history of this cluster.
Twenty Years of Timing SS 433 Eikenberry, S. S; Cameron, P. B; Fierce, B. W ...
Astrophysical journal/The Astrophysical journal,
11/2001, Volume:
561, Issue:
2
Journal Article
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