Table of contents

In this paper, we present some correlations of neutral hydrogen (H i) gas and physical properties of galaxies to investigate the role of atomic gas in governing galaxy evolution. We build a H i-detected sample including 70 galaxies that are detected by ALFALFA in a 15 deg² region, and derive their star formation distribution based on the images of Hα narrowband observed here. In general, H i-detected galaxies have low surface density of stellar mass and active star formation. Additionally, most of the galaxies are in good agreement with the star-forming main sequence, consistent with the previous findings. We confirm the dependence of star formation (SF) in galaxies on H i gas at least on global scale, i.e., star formation rate (SFR) generally increases with H i mass, specific star formation rate (SSFR ≡ SFR/M_*) increases with H i fraction (f_{H i}) even for a given stellar mass, and H i-based star formation efficiency (SFE) mildly increases with the stellar mass and SFR surface density. Based on the distribution of stellar mass and star formation, we calculate the morphology indices of the sample, and analyze the dependence of f_{H i} and SFE on them. The weak correlations between SFE and morphological indexes imply a weak physical link between H i and star formation in small scale. We find that f_{H i} mildly increases with the asymmetry and decreases with the concentration of galaxies, suggesting that the H i gas supply and its effect are likely correlated with external processes in the extended disks of galaxies.

V341 Arae is a 10th-magnitude variable star in the southern hemisphere, discovered over a century ago by Henrietta Leavitt, but relatively little studied since then. Although historically considered to be a Cepheid, it is actually blue and coincides with an X-ray source. The star lies near the edge of the large, faint Hα nebula Fr 2–11, discovered by D. Frew, who showed that V341 Ara is actually a cataclysmic variable (CV). His deep imaging of the nebula revealed a bow-shock morphology in the immediate vicinity of the star. We have carried out spectroscopic monitoring of V341 Ara, and we confirm that it is a nova-like CV, with an orbital period of 0.15216 days (3.652 hr). We show that V341 Ara is remarkably similar to the previously known BZ Cam, a nova-like CV with a nearly identical orbital period, associated with the bow shock nebula EGB 4. Archival sky-survey photometry shows that V341 Ara normally varies between V ≃ 10.5 and 11, with a characteristic timescale ranging from about 10 to 16 days. V341 Ara lies well off-center within Fr 2–11. We speculate that either the star is undergoing a chance high-speed encounter with a small interstellar cloud, or that the nebula was ejected from the star itself in a nova outburst in the fairly distant past. At a distance of only 156 pc, V341 Ara is one of the nearest and brightest known nova-like variables, and we encourage further studies.

To understand the formation and composition of planetary systems it is important to study their host stars composition since both are formed in the same stellar nebula. In this work, we analyze the behaviour of chemical abundances of Cu, Zn, Sr, Y, Zr, Ba, Ce, Nd, and Eu in the large and homogeneous HARPS-GTO planet search sample (R ∼ 115000). This sample is composed of 120 stars hosting high-mass planets, 29 stars hosting exclusively Neptunians and Super-Earths and 910 stars without detected giant planets. We compare the [X/Fe] ratios of such elements in different metallicity bins and we find that planet hosts present higher abundances of Zn for [Fe/H] < −0.1 dex. On the other hand, Ba, Sr, Ce, and Zr abundances are underabundant in stars with planets, with a bigger difference for stars only hosting low-mass planets. However, most of the offsets found can be explained by differences in stellar parameters and by the fact that planet hosts at low metallicity mostly belong to the Galactic thick disk. Only in the case of Ba we find a statistically significant (3σ) underabundance of 0.03 dex for low-mass planet hosts. The origin of these elements is quite complex due to their evolution during the history of the Galaxy. Therefore, it is necessary to understand and characterize the stellar populations to which planet hosts belong in order to do a fair comparison with stars without detected planets. This work demonstrates that the effects of Galactic chemical evolution and not the presence of planets mostly account for the differences we find.

V393 Scorpii is a member of the subclass of Algols dubbed double periodic variables (DPVs). These are semi-detached binaries with B-type primaries showing a long photometric cycle, lasting on average 33 times the orbital period. We describe the behavior of unreported metallic emission lines in the cool stellar component of this system. The emissions can be single or double for a same line, and they sometimes show velocity shifts regarding the velocity of the center of mass of the star. In addition, these lines are stronger during the high state. This behavior suggests the presence of active regions in the surface of the rapidly rotating A7 donor covering a fraction of the visible hemisphere, which have larger emissivity during the high state. Our finding supports the recently proposed dynamo model for the long cycle of DPVs proposed by Schleicher & Mennickent. The model predicts an increase of the dynamo number of the donor during epochs of mass transfer in this system, and a theoretical long/orbital period ratio very close to the observed one at the present system age.

We find that the emission-line object OGLEJ005039.05-725751.4, a member of the cluster OGLE-CL SMC 64, exhibits a peculiar light curve pattern repeating with a recurrence time of 141.45 days. The light curve resembles periodic outbursts with a duty cycle of 20%. A second long cycle of 2500 days is also detected in the photometric data set. Two X-SHOOTER spectra obtained at minimum and maximum reveal a Be star dominating at minimum light resembling the Classical Be star 48 Lib. The larger Hα emission, the stronger Na D absorption and the appearance of emission in the infrared Ca II triplet at maximum, might indicate periodic mass transfer in a complex binary system.

We present the Spectral Image Typer (SPIT), a convolutional neural network (CNN) built to classify spectral images. In contrast to traditional, rules-based algorithms that rely on metadata provided with the image (e.g., header cards), SPIT is trained solely on the image data. We have trained SPIT on 2004 human-classified images taken with the Kast spectrometer at Lick Observatory with types of Bias, Arc, Flat, Science, and Standard. We include several preprocessing steps (scaling, trimming) motivated by human practice and also expanded the training set to balance between image type and increase diversity. The algorithm achieved an accuracy of 98.7% on the held-out validation set and an accuracy of 98.7% on the test set of images. We then adopt a slightly modified classification scheme to improve robustness at a modestly reduced cost in accuracy (98.2%). The majority of mis-classifications are Science frames with very faint sources confused with Arc images (e.g., faint emission line galaxies) or Science frames with very bright sources confused with Standard stars. These are errors that even a well-trained human is prone to make. Future work will increase the training set from Kast, will include additional optical and near-IR instruments, and may expand the CNN architecture complexity. We are now incorporating SPIT in the PYPIT data reduction pipeline (DRP) and are willing to facilitate its inclusion in other DRPs.

We explore the feasibility of using current generation, off-the-shelf, indium gallium arsenide (InGaAs) near-infrared (NIR) detectors for astronomical observations. Light-weight InGaAs cameras, developed for the night vision industry and operated at or near room temperature, enable cost-effective new paths for observing the NIR sky, particularly when paired with small telescopes. We have tested an InGaAs camera in the laboratory and on the sky using 12 and 18 inch telescopes. The camera is a small-format, 320 × 240 pixels of 40 μm pitch, shortwave infrared (SWIR) device from Sensors Unlimited. Although the device exhibits a room-temperature dark current of 5.7 × 10⁴${e}^{-}\,{{\rm{s}}}^{-1}$ per pixel, we find observations of bright sources and low-positional-resolution observations of faint sources remain feasible. We can record unsaturated images of bright (J = 3.9) sources due to the large pixel well-depth and resulting high dynamic range. When mounted on an 18 inch telescope, the sensor is capable of achieving milli-magnitude precision for sources brighter than J = 8. Faint sources can be sky-background-limited with modest thermoelectric cooling. We can detect faint sources (J = 16.4 at 10σ) in a one-minute exposure when mounted to an 18 inch telescope. From laboratory testing, we characterize the noise properties, sensitivity, and stability of the camera in a variety of different operational modes and at different operating temperatures. Through sky testing, we show that the (unfiltered) camera can enable precise and accurate photometry, operating like a filtered J-band detector, with small color corrections. In the course of our sky testing, we successfully measured sub-percent flux variations in an exoplanet transit. We have demonstrated an ability to detect transient sources in dense fields using image subtraction of existing reference catalogs.

We present the photometric characterization of the four iXon Ultra 888 CCD cameras of the SPARC4 instrument, which will be installed on the 1.6 m telescope of the Pico dos Dias Observatory in Brazil. We applied experimental methodologies for a systematic characterization of the read noise, electronic gain, dark current, and quantum efficiency of the CCDs. We have analyzed the statistical distribution of the read noise, and also its spatial gradient and temporal variability, where we obtained an average value of the read noise of 6.33 electrons. We applied the Janesick method to determine the electronic gain, where we obtained an average value of 3.35 e-/ADU. We have also obtained an average dark current of 0.00014 e- pix⁻¹ s⁻¹ for CCD internal temperature of −70 °C. We have inspected the dependency of the dark current with temperature and the spatial distribution of the dark current, where we found a variable profile in the CCD 9917. We developed an experiment using a bench-mounted monochromator to obtain the spectral dependency of the quantum efficiency in the spectral range between 350 nm and 1100 nm, where we measured the quantum efficiency for each camera. The camera 9915 presents the highest quantum efficiency of 95.8%. Our results are compared with those from the manufacturer. These experiments allow us to diagnose the performance of these CCD cameras, an important sub-system of the SPARC4 instrument. It also provides a systematic way for monitoring the aging of the CCDs.

We present a new global array of small aperture optical telescopes designed to study artificial satellites and the nearby universe: the Falcon Telescope Network (FTN). Developed by the Center for Space Situational Awareness Research in the Department of Physics at the United States Air Force Academy (USAFA), the FTN is composed of 12 observatories in the United States, Chile, Germany, and Australia, with a potential site in South Africa. The observatory sites were strategically selected with the main objective that once in operation, the telescopes will be capable of working together to perform simultaneous and/or continuous observations of a single object in the sky. This capability allows the observation of artificial satellites from different baselines in a wide range of orbits, continuous data acquisition of variable astronomical sources, and rapid response observations of transient phenomena that require almost immediate follow-up (gamma-ray bursts, novae, or supernovae, etc.). Consisting of commercially available equipment, each observatory is equipped with a 0.5 m primary mirror telescope, a CCD camera, photometric filters, including a special filter to detect exoplanets, and a diffraction grating. The FTN is designed for remote and robotic operation with a host of automation software and services housed on the site computers and at USAFA. FTN partners will have access to a web-based interface where both the observation application as well as the raw data obtained by any of the Falcon nodes will be available. The FTN is a collaborative effort between the USAFA and educational or research institutions on four continents, demonstrating that, through the cooperation of multiple institutions of different levels and capabilities, high-level scientific and educational programs can be carried out, regardless of the geographic location of the various network members.