ABSTRACT
We describe our spectroscopic follow-up to the Local Group Galaxy Survey (LGGS) photometry of M31 and M33. We have obtained new spectroscopy of 1895 stars, allowing us to classify 1496 of ...them for the first time. Our study has identified many foreground stars, and established membership for hundreds of early- and mid-type supergiants. We have also found nine new candidate luminous blue variables and a previously unrecognized Wolf–Rayet star. We republish the LGGS M31 and M33 catalogs with improved coordinates, and including spectroscopy from the literature and our new results. The spectroscopy in this paper is responsible for the vast majority of the stellar classifications in these two nearby spiral neighbors. The most luminous (and hence massive) of the stars in our sample are early-type B supergiants, as expected; the more massive O stars are more rare and fainter visually, and thus mostly remain unobserved so far. The majority of the unevolved stars in our sample are in the 20–40
M
⊙
range.
ABSTRACT
We report a study exploring how the use of deep neural networks with astronomical Big Data may help us find and uncover new insights into underlying phenomena: through our experiments ...towards unsupervised knowledge extraction from astronomical Big Data we serendipitously found that deep convolutional autoencoders tend to reject telluric lines in stellar spectra. With further experiments, we found that only when the spectra are in the barycentric frame does the network automatically identify the statistical independence between two components, stellar versus telluric, and rejects the latter. We exploit this finding and turn it into a proof-of-concept method for removal of the telluric lines from stellar spectra in a fully unsupervised fashion: we increase the interobservation entropy of telluric absorption lines by imposing a random, virtual radial velocity to the observed spectrum. This technique results in a non-standard form of ‘whitening’ in the atmospheric components of the spectrum, decorrelating them across multiple observations. We process more than 250 000 spectra from the High Accuracy Radial velocity Planetary Search and with qualitative and quantitative evaluations against a data base of known telluric lines, show that most of the telluric lines are successfully rejected. Our approach, ‘Stellar Karaoke’, has zero need for prior knowledge about parameters such as observation time, location, or the distribution of atmospheric molecules and processes each spectrum in milliseconds. We also train and test on Sloan Digital Sky Survey and see a significant performance drop due to the low resolution. We discuss directions for developing tools on top of the introduced method in the future.
We observed nine primary transits of the hot Jpiter TrES-3b in several optical and near-UV photometric bands from 2009 June to 2012 April in an attempt to detect its magnetic field. Vidotto, Jardine ...and Helling suggest that the magnetic field of TrES-3b can be constrained if its near-UV light curve shows an early ingress compared to its optical light curve, while its egress remains unaffected. Predicted magnetic field strengths of Jpiter-like planets should range between 8 G and 30 G. Using these magnetic field values and an assumed B
* of 100 G, the Vidotto et al. method predicts a timing difference of 5-11 min. We did not detect an early ingress in our three nights of near-UV observations, despite an average cadence of 68 s and an average photometric precision of 3.7 mmag. However, we determined an upper limit of TrES-3b's magnetic field strength to range between 0.013 and 1.3 G (for a 1-100 G magnetic field strength range for the host star, TrES-3) using a timing difference of 138 s derived from the Nyquist-Shannon sampling theorem. To verify our results of an abnormally small magnetic field strength for TrES-3b and to further constrain the techniques of Vidotto et al., we propose future observations of TrES-3b with other platforms capable of achieving a shorter near-UV cadence. We also present a refinement of the physical parameters of TrES-3b, an updated ephemeris and its first published near-UV light curve. We find that the near-UV planetary radius of R
p = 1.386+ 0.248
− 0.144 R
Jup is consistent with the planet's optical radius.
Transits of exoplanets observed in the near-UV have been used to study the scattering properties of their atmospheres and possible star–planet interactions. We observed the primary transits of 15 ...exoplanets (CoRoT-1b, GJ436b, HAT-P-1b, HAT-P-13b, HAT-P-16b, HAT-P-22b, TrES-2b, TrES-4b, WASP-1b, WASP-12b, WASP-33b, WASP-36b, WASP-44b, WASP-48b, and WASP-77Ab) in the near-UV and several optical photometric bands to update their planetary parameters, ephemerides, search for a wavelength dependence in their transit depths to constrain their atmospheres, and determine if asymmetries are visible in their light curves. Here, we present the first ground-based near-UV light curves for 12 of the targets (CoRoT-1b, GJ436b, HAT-P-1b, HAT-P-13b, HAT-P-22b, TrES-2b, TrES-4b, WASP-1b, WASP-33b, WASP-36b, WASP-48b, and WASP-77Ab). We find that none of the near-UV transits exhibit any non-spherical asymmetries, this result is consistent with recent theoretical predictions by Ben-Jaffel et al. and Turner et al. The multiwavelength photometry indicates a constant transit depth from near-UV to optical wavelengths in 10 targets (suggestive of clouds), and a varying transit depth with wavelength in 5 targets (hinting at Rayleigh or aerosol scattering in their atmospheres). We also present the first detection of a smaller near-UV transit depth than that measured in the optical in WASP-1b and a possible opacity source that can cause such radius variations is currently unknown. WASP-36b also exhibits a smaller near-UV transit depth at 2.6σ. Further observations are encouraged to confirm the transit depth variations seen in this study.
ABSTRACT We describe our spectroscopic follow-up to the Local Group Galaxy Survey (LGGS) photometry of M31 and M33. We have obtained new spectroscopy of 1895 stars, allowing us to classify 1496 of ...them for the first time. Our study has identified many foreground stars, and established membership for hundreds of early- and mid-type supergiants. We have also found nine new candidate luminous blue variables and a previously unrecognized Wolf-Rayet star. We republish the LGGS M31 and M33 catalogs with improved coordinates, and including spectroscopy from the literature and our new results. The spectroscopy in this paper is responsible for the vast majority of the stellar classifications in these two nearby spiral neighbors. The most luminous (and hence massive) of the stars in our sample are early-type B supergiants, as expected; the more massive O stars are more rare and fainter visually, and thus mostly remain unobserved so far. The majority of the unevolved stars in our sample are in the 20-40 M range.
Our understanding of galaxies is limited by our place within the Milky Way and the vast distances to external galaxies. However, our proximity to the Magellanic Clouds, a pair of nearby galaxies in ...our Galaxy’s halo, provides an opportunity to closely examine and survey a galactic system. Many surveys have been conducted of this system, giving a thorough look into some components of the galaxies and providing constraints to dynamic models of the system. But surveys of the ionized gas throughout the Magellanic System have been primarily limited to bright H II regions near young, hot stars and the energetic remnants of recent supernovae. Using the Wisconsin H-Alpha Mapper (WHAM), I have conducted the first survey of diffuse ionized gas throughout the extended Magellanic System, adding an essential view of a key component. First, I present the first extended diffuse ionized gas map of the Small Magellanic Cloud, which includes new kinematic information about the motion of this gas far from the center of the galaxy. Using these results, I calculate the first estimate of the total ionized gas around the SMC. Next, I present a survey of the Large Magellanic Cloud. Using methods developed from the Small Magellanic Cloud survey, I present the first extended diffuse ionized gas maps of the Large Magellanic Cloud and calculated the total ionized gas mass. Finally, I discuss the initial results of an H-alpha survey of Magellanic Stream that I designed and carried out. Covering a large region of the sky (40 by 120 degrees), this is the first attempt to detect and characterize the full extent of ionized gas within the Magellanic Stream. To highlight the progress of the survey reduction, I present four regions along the Stream and compare emission from neutral and ionized components. Together, these studies give new insight into the complex structure of the Magellanic System, explore the warm ionized medium in an interacting galactic system with unprecedented sensitivity, and produce new, more accurate estimates of the total ionized gas mass around the galaxies, providing important constraints for dynamic models of the system.
We report a study exploring how the use of deep neural networks with astronomical Big Data may help us find and uncover new insights into underlying phenomena: through our experiments towards ...unsupervised knowledge extraction from astronomical Big Data we serendipitously found that deep convolutional autoencoders tend to reject telluric lines in stellar spectra. With further experiments we found that only when the spectra are in the barycentric frame does the network automatically identify the statistical independence between two components, stellar vs telluric, and rejects the latter. We exploit this finding and turn it into a proof-of-concept method for removal of the telluric lines from stellar spectra in a fully unsupervised fashion: we increase the inter-observation entropy of telluric absorption lines by imposing a random, virtual radial velocity to the observed spectrum. This technique results in a non-standard form of ``whitening'' in the atmospheric components of the spectrum, decorrelating them across multiple observations. We process more than 250,000 spectra from the High Accuracy Radial velocity Planetary Search (HARPS) and with qualitative and quantitative evaluations against a database of known telluric lines, show that most of the telluric lines are successfully rejected. Our approach, `Stellar Karaoke', has zero need for prior knowledge about parameters such as observation time, location, or the distribution of atmospheric molecules and processes each spectrum in milliseconds. We also train and test on Sloan Digital Sky Survey (SDSS) and see a significant performance drop due to the low resolution. We discuss directions for developing tools on top of the introduced method in the future.
Observations with the Wisconsin H-alpha Mapper (WHAM) reveal a large, diffuse ionized halo that surrounds the Small Magellanic Cloud (SMC). We present the first kinematic H-alpha survey of an ...extended region around the galaxy, from (l,b) = (289.5,-35.0) to (315.1,-5.3) and covering +90 <= vLSR <= +210 km s-1. The ionized gas emission extends far beyond the central stellar component of the galaxy, reaching similar distances to that of the diffuse neutral halo traced by 21 cm observations. H-alpha emission extends several degrees beyond the sensitivity of current H I surveys toward smaller Galactic longitudes and more negative Galactic latitudes. The velocity field of the ionized gas near the SMC appears similar to to the neutral halo of the galaxy. Using the observed emission measure as a guide, we estimate the mass of this newly revealed ionized component to be roughly (0.8 - 1.0) x 10^9 M_sun, which is comparable to the total neutral mass in the same region of (0.9 - 1.1) x 10^9 M_sun. We find ratios of the total ionized gas mass divided by the total neutral plus ionized gas mass in three distinct subregions to be: (1) 46%-54% throughout the SMC and its extended halo, (2) 12%-32% in the SMC Tail that extends toward the Magellanic Bridge, and (3) 65%-79% in a filament that extends away from the SMC toward the Magellanic Stream. This newly discovered, coherent H-alpha filament does not appear to have a well-structured neutral component and is also not coincident with two previously identified filaments traced by 21 cm emission within the Stream.
We describe our spectroscopic follow-up to the Local Group Galaxy Survey (LGGS) photometry of M31 and M33. We have obtained new spectroscopy of 1895 stars, allowing us to classify 1496 of them for ...the first time. Our study has identified many foreground stars, and established membership for hundreds of early- and mid-type supergiants. We have also found 9 new candidate Luminous Blue Variables and a previously unrecognized Wolf-Rayet star. We republish the LGGS M31 and M33 catalogs with improved coordinates and including spectroscopy from the literature and our new results. The spectroscopy in this paper is responsible for the vast majority of the stellar classifications in these two nearby spiral neighbors. The most luminous (and hence massive) of the stars in our sample are early-type B supergiants, as expected; the more massive O stars will be fainter visually, and thus mostly remain unobserved so far. The majority of the unevolved stars in our sample are in the 20-40Mo range.
Transits of exoplanets observed in the near-UV have been used to study the scattering properties of their atmospheres and possible star-planet interactions. We observed the primary transits of 15 ...exoplanets (CoRoT-1b, GJ436b, HAT-P-1b, HAT-P-13b, HAT-P-16b, HAT-P-22b, TrES-2b, TrES-4b, WASP-1b, WASP-12b, WASP-33b, WASP-36b, WASP-44b, WASP-48b, and WASP-77Ab) in the near-UV and several optical photometric bands to update their planetary parameters, ephemerides, search for a wavelength dependence in their transit depths to constrain their atmospheres, and determine if asymmetries are visible in their light curves. Here we present the first ground-based near-UV light curves for 12 of the targets (CoRoT-1b, GJ436b, HAT-P-1b, HAT-P-13b, HAT-P-22b, TrES-2b, TrES-4b, WASP-1b, WASP-33b, WASP-36b, WASP-48b, and WASP-77Ab). We find that none of the near-UV transits exhibit any non-spherical asymmetries, this result is consistent with recent theoretical predictions by Ben-Jaffel et al. and Turner et al. The multi-wavelength photometry indicates a constant transit depth from near-UV to optical wavelengths in 10 targets (suggestive of clouds), and a varying transit depth with wavelength in 5 targets (hinting at Rayleigh or aerosol scattering in their atmospheres). We also present the first detection of a smaller near-UV transit depth than that measured in the optical in WASP-1b and a possible opacity source that can cause such radius variations is currently unknown. WASP-36b also exhibits a smaller near-UV transit depth at 2.6\(\sigma\). Further observations are encouraged to confirm the transit depth variations seen in this study.
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