INSTRUMENT | One Antarctic Night (IOAN) is an interactive generative virtual environment created utilizing data captured by the AST3 robotic telescopes on Dome A in Antarctica (Ma et al., 2020), in combination with open astronomical data from the GAIA DR2 release (https://www.cosmos.esa.int/web/gaia) (Gaia Collaboration, 2016; Gaia Collaboration et al., 2018), and the SIMBAD Astronomical Database (http://simbad.u-strasbg.fr/simbad/) (Wenger et al., 2000).

Subsections:

1. AST3 Robotic Telescope - Dome A, Antarctica
2. AST3 Dataset: Large Magellanic Cloud (LMC)
3. Analysis Results That Are Returned Into The Artwork Contribution to Knowledge
4. References

AST3 data is provided by astrophysicist Lifan Wang, of Texas A&M, a scientific collaborator for this project (https://mitchell.tamu.edu/people/Lifan-Wang/) and PI of the AST3 observatory on Antarctica. Broadly, Lifan's research is focused on understanding the nature of dark matter/dark energy in the universe, developing an understanding of galactic structure and formation, and developing a cosmic distance ladder.

The AST3 (Antarctica Schmidt Telescopes) robotic telescopes are located on Dome A (Dome Argus) Antarctica near the geographic South Pole(Yuan and Su, 2012). Dome A is the highest peak on the Antarctic plateau at an elevation of 4,091 meters (13,422 ft), and one of the best sites on Earth for ground-based optical/infrared astronomical observations(Ma et al., 2012a). The observatory is an international collaboration between the USA, Australia and China. Observations in the infrared and near infrared region of the electromagnetic spectrum collected by AST3 require clear skies with low atmospheric blurring, and low background sky brightness. Antarctica's continuous darkness for almost 4 months, cold and dry air conditions, and the low turbulence in Earth's atmosphere make Dome A well suited for astronomical observation of faint/distant objects. Time domain astronomy/scientific objectives of the AST3 survey include observation of various classes of super novae; continuous monitoring of the Large Magellanic Cloud (LMC) for detection of variable objects, microlensing and transient (short duration) events and research into the nature of dark matter; observations of RR Lyrae and Cepheid variable stars, considered as standards of known distance and luminosity for developing a cosmic distance ladder and understanding galactic structure. Lifan's publications from AST3 include detection of variable stars within the Galactic disk(Li, Fu and Liu, 2015; Wang et al., 2017).The first AST3 telescope was installed on Dome A in January 24, 2012, and its operation began on March 15, 2012(Yuan et al., 2016).

For IOAN, Lifan provided some of the first data to be collected by the telescopes. It is unpublished and not accessible to the general public. It consists of time series photometry observations in the near infrared ( i band) for 817,373 astronomical objects at the center of the Large Magellanic Cloud (LMC) captured by the AST3 robotic telescope during its first observing season. We cross-referenced the AST3-LMC data with data from GAIA DR2 and SIMBAD open access astronomical data catalogs. Data was retrieved utilizing queries by matching galactic (RA, Dec) coordinates for the AST3-LMC astronomical objects to those in both GAIA DR2 and SIMBAD. Operated by the European Space Agency (ESA), GAIA is a space-borne observatory (two telescopes, three functions – astrometry, photometry, spectrometry) with a scientific mission of capturing measurements on over one billion astronomical objects, including position, photometry and spectroscopy to create a 3D map of the Milky Way galaxy(ESA Science & Technology - Gaia, no date). SIMBAD is an astronomical database that cross-references astronomical data with bibliographic information(SIMBAD Astronomical Database - CDS (Strasbourg), no date).

To give a sense of the remoteness of the site, and the scale of the undertaking that this science requires, I am inserting several images below from a TAMU news release about the installation of the AST3 telescope. Additionally, I am including figures from (Ma et al., 2012a) showing the CCD detector for the telescope, and another from Zhaohui Shang's presentation at the 2013 Scientific Committee on Antarctic Research annual meeting, and workshop on Astronomy and Astrophysics from Antarctica (AAA). http://www.astronomy.scar.org/AAA2013/pdf/Shang.pdf and http://www.astronomy.scar.org/AAA2013/

The AST3 robotic telescope has tracking and pointing hardware/software, and a sensor of 10560 x 10560 CCD pixels, Each pixel corresponds to 1 arcsecond (equal to 1/3600 of a degree). The filter used for the observations is the " i band" (near infrared). There is no mechanical shutter mechanism. Instead the CCD is divided into an image area (central portion of two stacked regions 10560 x 2640 each) and two frame store regions of 10560x2640 each, one at the top and bottom. Data from the image area is transferred out onto each of the storage regions to terminate an exposure (Ma et al., 2012b; Li, Fu and Liu, 2015; Wang et al., 2017).

Figure: Slide from Z. Shang, 2013 AST3 Survey update presentation at SCAR AAA meeting, showing the AST3 telescope CCD frame transfer functionality. Source: http://www.astronomy.scar.org/AAA2013/pdf/Shang.pdf

The AST3-LMC data provided has the following format: For a given object ID, such as AST3 40005033, the object has observations on a series of dates/times (specified as Modified Julian Date), an x, y position on the telescope CCD sensor, and a magnitude reading in the near-infrared (i mag). Modified Julian dates are a version of the Julian date system used by astronomers. Both Julian or MJD systems number days sequentially, and provide an unambiguous date and time for astronomical events expressed as a number and fraction of a day (Ridpath, 2018a, 2018b).

Date (MJD)	X	Y	Magnitude
56043.10036	3273.215	2387.867	15.6147
56043.10554	3274.517	2388.812	15.6194
56044.08142	3265.545	2358.946	15.6747
56044.08365	3270.285	2359.819	15.6822
56044.08735	3270.882	2359.571	15.6504

Table: Sample of AST3-LMC time series data for astronomical object ID 40005033. The initial data provided only supplied numerical data, and no telescope images or object coordinates.

In addition, image data from the telescope was obtained and the corresponding RA (right ascension) and Dec (declination) coordinates for all of the objects in the dataset. RA, Dec galactic coordinates serve as a unique identifier for astronomical objects.

Figure: a0329.160.fit, mjd 56048.0479629 – 817, 373 objects, LMC – image from the AST3 telescope dataset from the center of the LMC

The first step in exploring and learning to work with the data was to confirm a match between the objects from their x,y locations on the telescope CCD sensor to the corresponding image data. To confirm an understanding of the spatial orientation of the coordinates in relation to the telescope data, an openGL render of the x,y positions as red + symbols was superimposed onto the telescope image data.

Figure:Render of object x,y telescope CCD coordinates from AST3 LMC data onto telescope image to confirm spatial relations.

This was the start of the process of exploring the dataset and its evocative potentials. There are a total of 4183 time stamps (image frames) in the dataset. Through image registration and partial overlaps 817,373 objects were identified from the 4183 time stamps within the data at LMC center. With an average of 927 measurements per object there are 758,457,209 magnitude readings in the dataset (Table row AST3-LMC - below). To connect the AST3 unpublished scientific data with open astronomical data, it is annotated with additional data by cross referencing to data from open repositories. This enriches the AST3-LMC data with additional dimensions for each object. RA, Dec coordinate queries into the GAIA DR2 archive and SIMBAD database were used to retrieve data for objects within less than 1.5 arc seconds from the queried coordinates . This yields a set of attributes for the AST3 LMC objects, beyond those which were within the time series photometry readings from the telescope (Table # rows GAIA DR2 and SIMBAD).

Table: Row 1: data from telescope sensor. Row 2: Celestial coordinates added to the data from the telescope and statistics computed. Row 3: AST3-LMC object celestial coordinates (RA, Dec) were utilized to query the GAIA DR2 catalog and SIMBAD database. Coordinate queries for the 817,373 AST3 objects identified 745,514 matches within less than 1.5 arc seconds within the GAIA DR2 catalog of over 1 billion objects. Row 4: Coordinate queries for the 817,373 AST3 objects identified 67,311 matches within less than 1.5 arc seconds within the SIMBAD database of 9,235,962 records.

In addition to annotating the data with cross-references into public catalogs, statistics are calculated for each object, such as Lomb-Scargle (LS) periodograms (Zechmeister and Kürster, 2009; Lomb-Scargle Periodograms — Astropy v2.0.4, no date). LS periodograms are routinely used in astronomy to reveal periodicity in irregularly sampled data. The data for AST3 is irregularly sampled. Periodicity is used to characterize the variation in brightness of an observed object to determine if the variation is an intrinsic characteristic of the object, or if it is due to other causes, such as effects of the Earth's atmosphere, satellite trails or interstellar dust etc. Some objects have repeating patterns of variability such as binary stars, or pulsating stars, others, such as supernovae have characteristic variability that is not repeating.

Distinguishing whether or not an object is variable, and what type of variable object it is, is an important aspect of the research aims for AST3, and a significant aspect of the work done by astronomers when characterizing astronomical objects. Exploring the AST3 data, and wrangling with how to identify evocative potentials in what is approximately a dataset of 758million magnitude values, with a position on a CCD sensor, or galactic coordinate and a time stamp, lead to learning about this aspect of the astronomical data-to-knowledge pipeline, while researching the tools and types of analyses astronomers used to process the raw data that Lifan provided.

A pivotal insight into the evocative and poetic potentials of the AST3 data occurred when it became apparent that a major metaphor for astronomical objects is that they are considered a source of "signal" in relation to an infinite expanse of background "noise" in the Universe. Not all objects are stars. Some are galaxies, nebulae, or star clusters, for example. Yet, irrespective of their structural classification, they each have a characteristic signal at a one or more wavelengths in the electromagnetic spectrum. What is "signal" and what is "noise" depends on what you are looking for, and the wavelength (region of the electromagnetic spectrum) that you are viewing the Universe through e.g. radio, infrared, optical, x-ray, or gamma-ray, for example. A given object has characteristic signal at each of these wavelength regions of the spectrum.

The notion of "object" and "signal", and the relationship of the data to the inherent nature of the objects, and how we perceive objects in context of the broader universe as we seek to understand the ultimate nature of reality, became a central theme around which the poetics, generative processes and interaction for IOAN are organized. This drives the mapping of analytical gestures onto interactive gestures in-world. The LS periodograms are part of the high-dimensional (dataremix) visual and auditory data mapping strategies in IOAN. They are an analytical process, part of the astronomical data-to-knowledge pipeline, that functions as an instance, one of a class of, interactive and poetic generative processes, as well as constraints upon, participant interaction within IOAN.

• identified cross-reference matches for 754,514 of the 817,373 AST3 LMC-center objects within GAIA DR2 ( 91 percent of AST3 objects matched). It's important to note that AST3 data was captured in 2012, and provided by Lifan for IOAN in 2016. GAIA DR2 data was released in April 2018.
• identified an additional 5,344,749 astronomical objects within the RA, Dec boundaries of the AST3-LMC-center dataset. These are objects not identified by AST3, but visible from GAIA since it is space borne.
• identified 52,413 cross-referenced objects in SIMBAD, or 6% of AST3 objects had existing identifications or publications/bibliographic records in SIMBAD. An additional 36,003 objects within SIMBAD fall within the RA, Dec boundaries of the AST3 dataset, yet did not cross match with coordinates for objects within our dataset. This is data about objects not captured by AST3, but which resides within the same region, and which was captured by other astronomical surveys.
• categorized cross-referenced AST3 objects as one of three variable classes: cross referenced to known variable object from SIMBAD, known variable from GAIA, but not also in SIMBAD, and AST3 object not cross-referenced to a known variable, LS periodogram is calculated and object is designated variable class as yet to be determined.
• Of these, 67,376 have a known variable type of Rrlyr (RR Lyrae), another 417 have a variable classification from GAIA, yet may be variable of unknown type. For 773,656 objects, the periodicity of the signal is computed using Lomb Scargle (Astropy(Astrostatistics Tools (astropy.stats) — Astropy v2.0.4, no date) and VarTools (Hartman and Bakos, 2016; The VARTOOLS Light Curve Analysis Program, no date)), and the variable class is designated as "TBD" and we display the period and phased light curve. This process served to confirm the variable classes of the AST3 data, and as part of the process of characterizing the AST3 dataset in regards to new variable objects. A future scientific publication will be prepared summarizing the results of this analysis.

From exploring the AST3 dataset, some descriptive values and ranges were calculated:

• AST3-LMC center range of observations per object: 1 to 6,694, over 4,183 frames (date/time stamp), for a total of 55 days (3/12/2012 – 5//2012). Conditions in Antarctica got so cold that the telescope froze for a part of the first observing season, prompting changes to its design for installation of a second AST3 telescope (See SCAR AAA presentation http://www.astronomy.scar.org/AAA2013/pdf/Shang.pdf
• GAIA DR2 objects: of 6,162,122 objects within the AST3-LMC RA, Dec boundaries, the range of observations is from 13 to 292 per object, photometry observations ranged from ~ 6 to 24 observations per objects. Measurements include g, bp, rp, flux and magnitude from the GAIA photometry function.
• RMS of the i mag value is computed and plotted in two color scatter plot to compare known variable objects (cross-referenced to known variables in GAIA/SIMBAD versus AST3 objects. The lightcurve rms (y axis) is plotted against the i mag (x axis) ranging from 6 to 20. The higher the magnitude value, the fainter the object.
• Signal to noise (S/N)ratio of the i mag is computed (RMS and S/N thresholds are used to identify potential candidates for variable objects)
• standard deviation of i mag is computed (Astropy and VarTools)
• folded light curve is computed and plotted (Astropy and VarTools)
• phased light curve is computed and plotted (Astropy and VarTools)
• Cross-reference of AST3 to GAIA retrieved Astrometric pseudocolor and the error for pseudocolor for 4,472,578 objects
• astrometric values from GAIA catalog are retrieved and matched e.g. parallax, proper motion in Ra, and Dec, effective temperature, spectral types, galaxy morphology etc. if known
• Approximately 350K of the AST3 objects had a primary LS period of 1 day or less, with the range of LS primary periodicity ranging from < 1 day to > 100 days.

A few notes on terminology in this section on data.

• magnitude is the apparent brightness of an object as it appears on Earth (from location of the detector)
• 1^stmagnitude: brightest stars visible to the human eye ( 100x than mag 6)
• 6^th magnitude: faintest stars visible by human eye
• For every 5 magnitudes difference in brightness of 2 objects, they differ by a factor of 100, so a 10 magnitude difference, means something is 10,000x fainter.
• to calculate absolute magnitude, one needs the distance to the object, and in learning about astronomy, it became apparent that something we take for granted, the ability to measure distance on Earth, is not straightforward in space. Part of Lifan's research is to develop a cosmic distance scale.

Results of cross-referencing and computing descriptive statistics is stored in mySQL database.

An overview of the data is recorded and done in multiple spreadsheets in addition to the SQL database. The overviews are part of the process of consolidating learning about the data and the science, in order to seek evolcative and poetic potentisl within it that can then be worked with through dataremix.

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