The unprecedented volume and rate of transient events that will be discovered by the Large Synoptic Survey Telescope (LSST) demand that the astronomical community update its follow-up paradigm. ...Alert-brokers-automated software system to sift through, characterize, annotate, and prioritize events for follow-up-will be critical tools for managing alert streams in the LSST era. The Arizona-NOAO Temporal Analysis and Response to Events System (ANTARES) is one such broker. In this work, we develop a machine learning pipeline to characterize and classify variable and transient sources only using the available multiband optical photometry. We describe three illustrative stages of the pipeline, serving the three goals of early, intermediate, and retrospective classification of alerts. The first takes the form of variable versus transient categorization, the second a multiclass typing of the combined variable and transient data set, and the third a purity-driven subtyping of a transient class. Although several similar algorithms have proven themselves in simulations, we validate their performance on real observations for the first time. We quantitatively evaluate our pipeline on sparse, unevenly sampled, heteroskedastic data from various existing observational campaigns, and demonstrate very competitive classification performance. We describe our progress toward adapting the pipeline developed in this work into a real-time broker working on live alert streams from time-domain surveys.
Based on CHARA Array measurements, we present the angular diameters of 23 nearby, main-sequence stars, ranging from spectral types A7 to K0, 5 of which are exoplanet host stars. We derive linear ...radii, effective temperatures, and absolute luminosities of the stars using Hipparcos parallaxes and measured bolometric fluxes. The new data are combined with previously published values to create an Angular Diameter Anthology of measured angular diameters to main-sequence stars (luminosity classes V and IV). This compilation consists of 125 stars with diameter uncertainties of less than 5%, ranging in spectral types from A to M. The large quantity of empirical data is used to derive color-temperature relations to an assortment of color indices in the Johnson (BVR sub(J)I sub(J)JHK), Cousins (R sub(C)I sub(C)), Kron (R sub(K)I sub(K)), Sloan (griz), and WISE (W sub(3)W sub(4)) photometric systems. These relations have an average standard deviation of ~3% and are valid for stars with spectral types A0-M4. To derive even more accurate relations for Sun-like stars, we also determined these temperature relations omitting early-type stars (T sub(eff) > 6750 K) that may have biased luminosity estimates because of rapid rotation; for this subset the dispersion is only ~2.5%. We find effective temperatures in agreement within a couple of percent for the interferometrically characterized sample of main-sequence stars compared to those derived via the infrared flux method and spectroscopic analysis.
THE VARIABLE SKY OF DEEP SYNOPTIC SURVEYS Ridgway, Stephen T; Matheson, Thomas; Mighell, Kenneth J ...
The Astrophysical journal,
11/2014, Letnik:
796, Številka:
1
Journal Article
Recenzirano
Odprti dostop
The discovery of variable and transient sources is an essential product of synoptic surveys. The alert stream will require filtering for personalized criteria-a process managed by a functionality ...commonly described as a Broker. In order to understand quantitatively the magnitude of the alert generation and Broker tasks, we have undertaken an analysis of the most numerous types of variable targets in the sky-Galactic stars, quasi-stellar objects (QSOs), active galactic nuclei (AGNs), and asteroids. It is found that the Large Synoptic Survey Telescope (LSST) will be capable of discovering ~10 super(5) high latitude (|b| > 20degrees) variable stars per night at the beginning of the survey. (The corresponding number for |b| < 20degrees is orders of magnitude larger, but subject to caveats concerning extinction and crowding.) However, the number of new discoveries may well drop below 100 per night within less than one year. The same analysis applied to GAIA clarifies the complementarity of the GAIA and LSST surveys. Discovery of AGNs and QSOs are each predicted to begin at ~3000 per night and decrease by 50 times over four years. Supernovae are expected at ~1100 per night, and after several survey years will dominate the new variable discovery rate. LSST asteroid discoveries will start at >10 super(5) per night, and if orbital determination has a 50% success rate per epoch, they will drop below 1000 per night within two years.
The bright star 55 Cancri is known to host five planets, including a transiting super-Earth. The study presented here yields directly determined values for 55 Cnc's stellar astrophysical parameters ...based on improved interferometry: R = 0.943 ? 0.010 R , T EFF = 5196 ? 24 K. We use isochrone fitting to determine 55 Cnc's age to be 10.2 ? 2.5 Gyr, implying a stellar mass of 0.905 ? 0.015 M . Our analysis of the location and extent of the system's habitable zone (HZ; 0.67-1.32 AU) shows that planet f, with period ~260 days and Msin i = 0.155 M Jupiter, spends the majority of the duration of its elliptical orbit in the circumstellar HZ. Though planet f is too massive to harbor liquid water on any planetary surface, we elaborate on the potential of alternative low-mass objects in planet f's vicinity: a large moon and a low-mass planet on a dynamically stable orbit within the HZ. Finally, our direct value for 55 Cancri's stellar radius allows for a model-independent calculation of the physical diameter of the transiting super-Earth 55 Cnc e (~2.05 ? 0.15 R {circled plus}), which, depending on the planetary mass assumed, implies a bulk density of 0.76 Delta *r{circled plus} or 1.07 Delta *r{circled plus}.
Abstract
We present
H
-band interferometric observations of the red supergiant (RSG) AZ Cyg that were made with the Michigan Infra-Red Combiner (MIRC) at the six-telescope Center for High Angular ...Resolution Astronomy (CHARA) Array. The observations span 5 yr (2011–2016), which offers insight into the short and long-term evolution of surface features on RSGs. Using a spectrum of AZ Cyg obtained with SpeX on the NASA InfraRed Telescope Facility (IRTF) and synthetic spectra calculated from spherical MARCS, spherical PHOENIX, and SAtlas model atmospheres, we derive
T
eff
is between 3972 K and 4000 K and
log
g
between −0.50 and 0.00, depending on the stellar model used. Using fits to the squared visibility and GAIA parallaxes, we measure its average radius
R
=
911
−
50
+
57
R
⊙
. Reconstructions of the stellar surface using our model-independent imaging codes SQUEEZE and OITOOLS.jl show a complex surface with small bright features that appear to vary on a timescale of less than one year and larger features that persist for more than one year. The 1D power spectra of these images suggest a characteristic size of 0.52–0.69
R
⋆
for the larger, long lived features. This is close to the values of 0.51–0.53
R
⋆
that are derived from 3D RHD models of stellar surfaces. We conclude that interferometric imaging of this star is in line with predictions of 3D RHD models but that short-term imaging is needed to more stringently test predictions of convection in RSGs.
(ProQuest: ... denotes formulae and/or non-USASCII text omitted) The late-type dwarf GJ 436 is known to host a transiting Neptune-mass planet in a 2.6 day orbit. We present results of our ...interferometric measurements to directly determine the stellar diameter (Rlow * = 0.455 + or - 0.018 R sub(middot in circle)) and effective temperature (T sub(EFF) = 3416 + or - 54 K). We combine our stellar parameters with literature time-series data, which allows us to calculate physical and orbital system parameters, including GJ 436's stellar mass (...), stellar density (...), planetary radius (...), and planetary mass (...), implying a mean planetary density of ... These values are generally in good agreement with previous literature estimates based on assumed stellar mass and photometric light curve fitting. Finally, we examine the expected phase curves of the hot Neptune GJ 436b, based on various assumptions concerning the efficiency of energy redistribution in the planetary atmosphere, and find that it could be constrained with Spitzer monitoring observations.
We have measured the angular diameters for a sample of 24 exoplanet host stars using Georgia State University's CHARA Array interferometer. We use these improved angular diameters together with ...Hipparcos parallax measurements to derive linear radii and to estimate the stars' evolutionary states.
Using two aspheric mirrors, it is possible to apodize a telescope beam without losing light or angular resolution: the output beam is produced by "remapping" the entrance beam to produce the desired ...light intensity distribution in a new pupil. We present the phase-induced amplitude apodization coronagraph (PIAAC) concept, which uses this technique, and show that it allows efficient direct imaging of extrasolar terrestrial planets with a small-sized telescope in space. The suitability of the PIAAC for exoplanet imaging is due to a unique combination of achromaticity, small inner working angle (about 1.5 lambda /d), high throughput, high angular resolution, and large field of view. Three-dimensional geometrical ray tracing is used to investigate the off-axis aberrations of PIAAC configurations and show that a field of view of more than 100 lambda /d in radius is available thanks to the correcting optics of the PIAAC. Angular diameter of the star and tip-tilt errors can be compensated for by slightly increasing the size of the occulting mask in the focal plane, with minimal impact on the system performance. Earth-sized planets at 10 pc can be detected in less than 30 s with a 4 m telescope. Wave-front quality requirements are similar to classical techniques.
GJ 581 is an M dwarf host of a multiplanet system. We use long-baseline interferometric measurements from the CHARA Array, coupled with trigonometric parallax information, to directly determine its ...physical radius to be 0.299 ? 0.010 R . Literature photometry data are used to perform spectral energy distribution fitting in order to determine GJ 581's effective surface temperature T EFF = 3498 ? 56 K and its luminosity L = 0.01205 ? 0.00024 L . From these measurements, we recompute the location and extent of the system's habitable zone and conclude that two of the planets orbiting GJ 581, planets d and g, spend all or part of their orbit within or just on the edge of the habitable zone.
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