Digital Sky Survey Research Articles

Evolutionary map of the universe (EMU): Observations of filamentary structures in the Abell S1136 galaxy cluster

Abstract We present radio observations of the galaxy cluster Abell S1136 at 888 MHz, using the Australian Square Kilometre Array Pathfinder radio telescope, as part of the Evolutionary Map of the Universe Early Science program. We compare these findings with data from the Murchison Widefield Array, XMM-Newton, the Wide-field Infrared Survey Explorer, the Digitised Sky Survey, and the Australia Telescope Compact Array. Our analysis shows the X-ray and radio emission in Abell S1136 are closely aligned and centered on the Brightest Cluster Galaxy, while the X-ray temperature profile shows a relaxed cluster with no evidence of a cool core. We find that the diffuse radio emission in the centre of the cluster shows more structure than seen in previous low-resolution observations of this source, which appeared formerly as an amorphous radio blob, similar in appearance to a radio halo; our observations show the diffuse emission in the Abell S1136 galaxy cluster contains three narrow filamentary structures visible at 888 MHz, between $\sim$ 80 and 140 kpc in length; however, the properties of the diffuse emission do not fully match that of a radio (mini-)halo or (fossil) tailed radio source.

Spectral Energy Distribution of Flares in the Variable Star AO Serpentis

Here we report on the flaring variable star AO Ser which was observed with the 0.4m SBIG optical telescope from Las Cumbres Obervatory Global Telescope Network remotely on 25/09/2022. The Spectrometric analysis was carried out with the SIMBAD Digital Sky Survey (DSS) menu from the VizieR GUI on the Aladin Software to obtain flux density, flare energy, flare wavelength and flare frequency. The light curve of AO Ser shows that the source has a strong presence of flares. Hence, we estimated the flare energy, flare wavelength and flare frequency of AO Ser at peak flares so as to deduce its spectral energy distribution. From the spectral energy distribution, the Aladin software automatically estimated the Flare Energy of AO Ser at(as) 1.09 2 e eV − , the Flare flux density of AO Ser F (ν ) at 3.27 1 e Jy + and Flare Flux Energy of AO Ser F (λ ) at 7.55 12 1 2 1 e erg cm m − −− − µ . We conclude that AO Ser is an eclipsing binary variable flaring stars that is losing mass in form of heat.

Discovery of a Surprising Flux Event in White Dwarf HZ 4

HZ 4 is a DA3.4C White Dwarf (WD) and a commonly used photometric standard star. While analyzing its suitability as a calibrator, data from TESS revealed an increase in flux by 43.2%, seen only on Sector 43 observed in 2021 September and October. The event duration is 28.8 hr, and the light curve shape is approximately symmetric and consists of a flux increase preceded and followed by a flux decrease of 11.4%. If periodic, the period would be >77 days. No other objects are observed in the Digital Sky Survey, Galaxy Evolution Explorer, or Wide-Field Infrared Explorer images within the TESS pixel in which HZ 4 resides. The event resembles the flux increases of long-lived WD pulsators, although HZ4 is not in the instability strip. There is no evidence of a binary companion, which suggests HZ4 is not a dwarf nova, nor photometric evidence of any circumstellar material.

Analysis of spin directions of galaxies in the DESI Legacy Survey

ABSTRACT The DESI Legacy Survey is a digital sky survey with a large footprint compared to other Earth-based surveys, covering both the Northern and Southern hemispheres. This paper shows the distribution of the spin directions of spiral galaxies imaged by DESI Legacy Survey. A simple analysis of dividing nearly 1.3 × 106 spiral galaxies into two hemispheres shows a higher number of galaxies spinning counterclockwise in the Northern hemisphere, and a higher number of galaxies spinning clockwise in the Southern hemisphere. That distribution is consistent with previous observations, but uses a far larger number of galaxies and a larger footprint. The larger footprint allows a comprehensive analysis without the need to fit the distribution into an a priori model, making this study different from all previous analyses of this kind. Fitting the spin directions of the galaxies to cosine dependence shows a dipole axis alignment with probability of P < 10−5. The analysis is done with a trivial selection of the galaxies, as well as simple explainable annotation algorithm that does not make use of any form of machine learning, deep learning, or pattern recognition. While further work will be required, these results are aligned with previous studies suggesting the possibility of a large-scale alignment of galaxy angular momentum.

Systematic biases when using deep neural networks for annotating large catalogs of astronomical images

Deep convolutional neural networks (DCNNs) have become the most common solution for automatic image annotation due to their non-parametric nature, good performance, and their accessibility through libraries such as TensorFlow. Among other fields, DCNNs are also a common approach to the annotation of large astronomical image databases acquired by digital sky surveys. One of the main downsides of DCNNs is the complex non-intuitive rules that make DCNNs act as a “black box”, providing annotations in a manner that is unclear to the user. Therefore, the user is often not able to know what information is used by the DCNNs for the classification. Here we demonstrate that the training of a DCNN is sensitive to the context of the training data such as the location of the objects in the sky. We show that for basic classification of elliptical and spiral galaxies, the sky location of the galaxies used for training affects the behavior of the algorithm, and leads to a small but consistent and statistically significant bias. That bias exhibits itself in the form of cosmological-scale anisotropy in the distribution of basic galaxy morphology. Therefore, while DCNNs are powerful tools for annotating images of extended sources, the construction of training sets for galaxy morphology should take into consideration more aspects than the visual appearance of the object. In any case, catalogs created with deep neural networks that exhibit signs of cosmological anisotropy should be interpreted with the possibility of consistent bias.

An Updated Small Magellanic Cloud and Magellanic Bridge Catalog of Star Clusters, Associations, and Related Objects

Abstract We present a catalog of star clusters, associations, and related extended objects in the Small Magellanic Cloud (SMC) and the Magellanic Bridge with 2741 entries, a factor 2 more than a previous version from a decade ago. Literature data up until 2018 December are included. The identification of star clusters was carried out with digital atlases in various bands currently available in the Digitized Sky Survey and the Machine Automatique à Mésurer pour l’Astronomie. imaging surveys. In particular, we cross-identified recent cluster samples from the Visible and Infrared Survey Telescope for Astronomy near-infrared YJK s survey of the Magellanic System, Optical Gravitational Lensing Experiment IV, and Survey of the MAgellanic Stellar History surveys, confirming new clusters and pointing out equivalencies. A major contribution of the present catalog consists of the accurate central positions for clusters and small associations, including a new sample of 45 clusters or candidates in the SMC and 19 in the Magellanic Bridge, as well as a compilation of the most reliable age and metallicity values from the literature. A general catalog must also deal with the recent discoveries of 27 faint and ultra-faint star clusters and galaxies projected on the far surroundings of the Clouds, most of them from the Dark Energy Survey. The information on these objects has been complemented with photometric, spectroscopic, and kinematical follow-up data from the literature. The underluminous galaxies around the Magellanic System, still very few as compared to the predictions from Λ Cold Dark Matter simulations, can bring constraints to galaxy formation and hierarchical evolution. Furthermore, we provide diagnostics, when possible, of the nature of the ultra-faint clusters, searching for borders of the Magellanic System extensions into the Milky Way gravitational potential.

Automatic detection of full ring galaxy candidates in SDSS

ABSTRACT A full ring is a form of galaxy morphology that is not associated with a specific stage on the Hubble sequence. Digital sky surveys can collect many millions of galaxy images, and therefore even rare forms of galaxies are expected to be present in relatively large numbers in image data bases created by digital sky surveys. Sloan Digital Sky Survey (SDSS) data release (DR) 14 contains ∼2.6 × 106 objects with spectra identified as galaxies. The method described in this paper applied automatic detection to identify a set of 443 ring galaxy candidates, 104 of them were already included in the Buta + 17 catalogue of ring galaxies in SDSS, but the majority of the galaxies are not included in previous catalogues. Machine analysis cannot yet match the superior pattern recognition abilities of the human brain, and even a small false positive rate makes automatic analysis impractical when scanning through millions of galaxies. Reducing the false positive rate also increases the true negative rate, and therefore the catalogue of ring galaxy candidates is not exhaustive. However, due to its clear advantage in speed, it can provide a large collection of galaxies that can be used for follow-up observations of objects with ring morphology.

The Lives and After Lives of Data

The most elusive term in data science is ‘data.’ While often treated as objects to be computed upon, data is a theory-laden concept with a long history. Data exist within knowledge infrastructures that govern how they are created, managed, and interpreted. By comparing models of data life cycles, implicit assumptions about data become apparent. In linear models, data pass through stages from beginning to end of life, which suggest that data can be recreated as needed. Cyclical models, in which data flow in a virtuous circle of uses and reuses, are better suited for irreplaceable observational data that may retain value indefinitely. In astronomy, for example, observations from one generation of telescopes may become calibration and modeling data for the next generation, whether digital sky surveys or glass plates. The value and reusability of data can be enhanced through investments in knowledge infrastructures, especially digital curation and preservation. Determining what data to keep, why, how, and for how long, is the challenge of our day.

Bok globule CB 17: polarization, extinction and distance

Abstract In this article, the results obtained from a polarimetric study of Bok globule CB 17 in both optical and submillimetre wavelengths are presented. Optical polarimetric observations in the R band (λ = 630 nm, Δλ = 120 nm) were conducted with the 1.04-m Sampurnanand Telescope, Aryabhatta Research Institute of observational sciencES (ARIES), in Nainital, India on 2016 March 9, while submillimetre polarimetric data are taken from the Submillimetre Common-User bolometer array POLarimeter (SCUPOL) data archive, which has been reanalysed. The contours of Herschel1 Spectral and Photometric Imaging Receiver (SPIRE) 500-μm dust continuum emission of CB 17 (typically a cometary-shaped globule) are overlaid on the Digital Sky Survey (DSS) image of CB 17 along with polarization vectors (optical and submm). The magnetic field strength at the core of the globule is estimated to be 99 μG. Using near-infrared photometric technique and Gaia data, the distance to CB 17 is found to be 253 ± 43 pc. The correlation between the various quantities of the globule is also studied. It is observed that the magnetic field in the cloud core as revealed by polarization measurements of the submillimetre dust emission is found to be almost aligned along the minor axis of the globule, which fits the magnetically regulated star formation model. A misalignment between core-scale magnetic field direction and molecular outflow direction is also found.

Long-Term Optical Monitoring of Blazars

Systematic monitoring of specific targets in the optical regime was historically applied on a very narrow sample of known variable stars. The discovery of blazars in the 20th century brought to the foreground the need for new global sky surveys, covering the entire sky and fainter sources. Full-sky surveys are conducted more easily from space observatories, while radio telescopes perform follow up observations from the ground. Blazars are detected in a wide range of energies, while they exhibit strong variability in various wavelengths from γ-rays and X-rays to the optical and radio domain. This results in a detailed classification, according to their emission properties in each region. The rapid variability in optical domain makes blazars interesting targets for optical sky surveys, offering a new opportunity to study their variability in the time domain. Digital sky surveys in optical and near-IR found a fertile ground with the aid of sensitive sensors. Only a few dedicated programs are focusing on blazar variability, a trend which evolved rapidly in the last decade. Modern techniques, in combination with dedicated sky survey programs lead towards a new era of long-term monitoring of blazars, aiming towards the search or variability on various time scales. In this work, an overview of blazar optical surveys and monitoring projects is given, addressing the major points of each one, and highlighting the constraints that the long-term study of blazars will bring through future international campaigns.

A Multi-band Catalog of 10978 Star Clusters, Associations, and Candidates in the Milky Way

Abstract We present a catalog of Galactic star clusters, associations and candidates with 10978 entries. This multi-band catalog was constructed over 20 years, starting with visual inspections on the Digital Sky Survey and incremented with the 2MASS, WISE, VVV, Spitzer, and Herschel surveys. Large and small catalogs, as well as papers on individual objects have been systematically cross-identified. The catalog provides Galactic and equatorial coordinates, angular diameters, and chronologically ordered designations, making it simple to assign discoveries and verify how often the objects were cataloged by different authors, search methods, and/or surveys. Detection in a single band is the minimum constraint to validate an entry. About 3200 objects have measured parameters in the literature. A fundamental contribution of the present study is to present an additional ≈7700 objects for the first analyses of nature, photometry, spectroscopy and structure. The present focus is not to compile or determine fundamental parameters, but to provide a catalog uniformly characterizing the entries. A major result is that now 4234 embedded clusters are cataloged, a factor of ≈1.5 larger than open clusters. In addition to cross-identifications in different references and wavelength domains, we also communicate the discovery of 638 star clusters and similar objects. The present general catalog provides previously studied objects and thousands of additional entries in a homogeneous way, a timely contribution to Gaia-related works.

A hybrid approach to machine learning annotation of large galaxy image databases

Abstract Modern astronomy relies on massive databases collected by robotic telescopes and digital sky surveys, acquiring data in a much faster pace than what manual analysis can support. Among other data, these sky surveys collect information about millions and sometimes billions of extra-galactic objects. Since the very large number of objects makes manual observation impractical, automatic methods that can analyze and annotate extra-galactic objects are required to fully utilize the discovery power of these databases. Machine learning methods for annotation of celestial objects can be separated broadly into methods that use the photometric information collected by digital sky surveys, and methods that analyze the image of the object. Here we describe a hybrid method that combines photometry and image data to annotate galaxies by their morphology, and a method that uses that information to identify objects that are visually similar to a query object (query-by-example). The results are compared to using just photometric information from SDSS, and to using just the morphological descriptors extracted directly from the images. The comparison shows that for automatic classification the image data provide marginal addition to the information provided by the photometry data. For query-by-example, however, the analysis of the image data provides more information that improves the automatic detection substantially. The source code and binaries of the method can be downloaded through the Astrophysics Source Code Library.

Photometry and spectroscopy of the luminous red nova PSNJ14021678+5426205 in the galaxy M101

We present the results of the study of the red nova PSN J14021678+5426205 based on the observations carried out with the Russian 6-m telescope (BTA) along with other telescopes of SAO RAS and SAI MSU. To investigate the nova progenitor, we used the data from the Digital Sky Survey and amateur photos available on the internet. In the period between April 1993 and July 2014, the brightness of the progenitor gradually increased by 2.2 mag in the V band. At the peak of the first outburst in mid-November of 2014, the star reached an absolute visual magnitude of -12.75 mag but was discovered later, in February 2015, in a repeated outburst at the absolute magnitude of -11.65 mag. The amplitude of the outburst was minimum among the red novae, only 5.6 mag in the V band. The H alpha emission line and the continuum of a cool supergiant with a gradually decreasing surface temperature were observed in the spectra. Such process is typical for red novae, although the object under study showed extreme parameters: maximum luminosity, maximum outburst duration, minimum outburst amplitude, unusual shape of the light curve. This event is interpreted as a massive OB star system components merging accompanied by the formation of a common envelope and then the expansion of this envelope with minimal energy losses.

New Planetary Nebulae Discovered by French Astrophotographs-Amateurs

Since 2012, French amateurs in astrophotography have been equipped with CCD imagers with high sensitivity and ∼1 arcsec resolution, allowing them to obtain images with high resolution and contrast, and with unprecedented depth, using narrow-band filters. On the other hand, they have been methodically scanning the digital sky survey (DSS), thereby visually identifying dozens of faint PN candidates in the Galaxy. These two methods lead to the discovery of 88 possible/probable PN. The large bipolar object Ou4 is one of the most interesting PN known.

DISCOVERY OF A BINARY BROWN DWARF AT 2 pc FROM THE SUN

I am using multi-epoch astrometry from the Wide-field Infrared Survey Explorer (WISE) to search for new members of the solar neighborhood via their high proper motions. Through this work, I have identified WISE J104915.57-531906.1 as a high proper motion object and have found additional detections in images from the Digitized Sky Survey, the Two Micron All-Sky Survey, and the Deep Near-Infrared Survey of the Southern Sky. I have measured a parallax of 0.496+/-0.037" (2.0+/-0.15 pc) from the astrometry in these surveys, making WISE J104915.57-531906.1 the third closest system to the Sun. During spectroscopic observations with GMOS at Gemini Observatory, an i-band acquisition image resolved it as a 1.5" (3 AU) binary. A spectrum was collected for the primary, which I classify as L8+/-1. The secondary is probably near the L/T transition as well given that it is only modestly fainter than the primary (delta i=0.45 mag).

Kn 26, a new quadrupolar planetary nebula

Once classified as an emission line source, the planetary nebula (PN) nature of the source Kn 26 has been only recently recognized in digital sky surveys. To investigate the spectral properties and spatio-kinematical structure of Kn 26, we have obtained high spatial-resolution optical and near-IR narrow-band images, high-dispersion long-slit echelle spectra, and intermediate-resolution spectroscopic observations. The new data reveal an hourglass morphology typical of bipolar PNe. A detailed analysis of its morphology and kinematics discloses the presence of a second pair of bipolar lobes, making Kn 26 a new member of the subclass of quadrupolar PNe. The time-lap between the ejection of the two pairs of bipolar lobes is much smaller than their dynamical ages, implying a rapid change of the preferential direction of the central engine. The chemical composition of Kn 26 is particularly unusual among PNe, with a low N/O ratio (as of type II PNe) and a high helium abundance (as of type I PNe), although not atypical among symbiotic stars. Such an anomalous chemical composition may have resulted from the curtail of the time in the Asymptotic Giant Branch by the evolution of the progenitor star through a common envelope phase.

Identification and properties of host galaxies of RCR radio sources

FIRST and NVSS radio maps are used to cross identify the radio sources of the RCR catalog, which is based on observational data obtained in several runs of the “Cold” survey, with the SDSS and DPOSS digital optical sky surveys and the 2MASS, LAS UKIDSS, and WISE infrared surveys. Digital images in various filters and the coadded gri-band SDSS images, red and infrared DPOSS images, JHK-band UKIDSS images, and JHK-band 2MASS images are analyzed for the sources with no optical candidates found in the above catalogs. Our choice of optical candidates was based on the data on the structure of the radio source, its photometry, and spectroscopy (where available). We found reliable identifications for 86% of the radio sources; possible counterparts for 8% of the sources, and failed to find any optical counterparts for 6% of the sources because their host objects proved to be fainter than the limiting magnitude of the corresponding surveys. A little over half of all the identifications proved to be galaxies; about one quarter were quasars, and the types of the remaining objects were difficult to determine because of their faintness. A relation between the luminosity and the radioloudness index was derived and used to estimate the 1.4 and 3.94 GHz luminosities for the sources with unknown redshifts. We found 3% and 60% of all the RCR radio sources to be FRI-type objects (L ≲ 1024 W/Hz at 1.4 GHz) and powerful FRII-type galaxies (L ≳ 1026.5 W/Hz), respectively, whereas the rest are sources including objects of the FRI, FRII, and mixed FRI-FRII types. Unlike quasars, galaxies show a trend of decreasing luminosity with decreasing flux density. Note that identification would be quite problematic without the software and resources of the virtual observatory.

Close neighbors of Markarian galaxies. I. Optical database

The catalogue of close neighbors of Markarian galaxies located inside of circles with radii 60 kpc from the centers of Markarian objects is presented, which combines extensive new measurements of their optical parameters with a literature and database search. The measurements were made using images extracted from the Digitized Sky Survey (DSS) Jpg (blue), Fpg (red) and Ipg (near-infrared) band photographic plates. We provide names, accurate coordinates, redshifts, morphological types, blue, red and near-infrared apparent magnitudes, apparent blue major diameters, axial ratios, as well as position angles for the neighbor galaxies. We also include their 2MASS infrared magnitudes. The total number of Markarian galaxies in the database is 274 and number of their neighbors is 359. The physical parameters of the systems of Markarian galaxies and their neighbors are determined and presented.

Far-infrared luminosity function of local star-forming galaxies in the AKARI Deep Field-South

We present a far-infrared galaxy luminosity function for the local universe. We have obtained 389 spectroscopic redshifts for galaxies observed at 90 microns in the AKARI Deep Field South, using the AAOmega fibre spectrograph via optical identifications in the digitized sky survey and 4m-class optical imaging. For the luminosity function presented in this paper, we have used those galaxies which have redshifts 0<z<0.25, have optical magnitudes and are not part of a newly discovered cluster of galaxies (giving a total of 130 sources). Infrared and optical completeness functions were estimated using earlier Spitzer data and APM B-band optical data respectively, and the luminosity function has been prepared using the 1/Vmax method. We also separate the luminosity function between galaxies which show evidence of predominantly star-forming activity and predominantly active galactic nucleus (AGN) activity in their optical spectra. Our luminosity function is in good agreement with the previous 90 micron luminosity function from the European Large Area ISO Survey, and we also present a luminosity function with combined AKARI and ISO data. The result is in reasonable agreement with predictions based on the earlier IRAS 60 micron PSC-z catalogue, and with a recent backward evolution model.

New faint planetary nebulae from the DSS and SDSS

AbstractHaving surveyed ≈ 10% of the sky, we have identified more than 130 PN candidates by surveying multicolour Digitized Sky Survey (DSS), Sloan Digitized Sky Survey (SDSS), and combined [O III], Hα and [S II] images. In a first imaging and spectroscopy campaign, 51 objects were identified as true and probable PNe. This work presents an additional 17 probable or possible PNe identified since that study. The majority of these candidates are situated at Galactic latitudes |b| &gt; 5^, with the exception of seven objects located closer to the Galactic plane. Using the techniques described here that do not require any new survey data, we anticipate that many more PNe are waiting to be found, perhaps as many as 90.