Source-linked AI summary
The All-Sky Automated Survey for Supernovae (ASAS-SN) Light Curve Server v1.0
C. S. Kochanek, B. J. Shappee, K. Z. Stanek, T. W. -S. Holoien, Todd A. Thompson, J. -L. Prieto, Subo Dong, J. V. Shields, D. Will, C. Britt, D. Perzanowski, G. Pojmanski
TL;DR
All-sky variability surveys need public access to extensive observations, but existing resources do not provide the same arbitrary-position coverage described here. This paper introduces a web tool that performs aperture photometry on ASAS-SN images in real time for user-specified coordinates. The result is up-to-date light-curve access across the celestial sphere, with slow execution and scope limitations that motivate future precomputed databases.
Problem
The paper addresses the need for publicly accessible all-sky variability data by extending ASAS-SN access beyond selected transient and variable-source samples.
Method
The web server accepts coordinates and a look-back time, performs aperture photometry on selected ASAS-SN images, and returns a graph and downloadable table.
Results
The server provides an up-to-date light curve for any point on the celestial sphere upon demand, with recent visible-position epochs generally less than a week old.
Takeaways & Limitations
The tool enables unbiased, current light-curve access for arbitrary sky positions as an initial step toward broader ASAS-SN public data products.
Abstract
from arXiv · showhide
The All-Sky Automated Survey for Supernovae (ASAS-SN) is working towards imaging the entire visible sky every night to a depth of V~17 mag. The present data covers the sky and spans ~2-5~years with ~100-400 epochs of observation. The data should contain some ~1 million variable sources, and the ultimate goal is to have a database of these observations publicly accessible. We describe here a first step, a simple but unprecedented web interface https://asas-sn.osu.edu/ that provides an up to date aperture photometry light curve for any user-selected sky coordinate. Because the light curves are produced in real time, this web tool is relatively slow and can only be used for small samples of objects. However, it also imposes no selection bias on the part of the ASAS-SN team, allowing the user to obtain a light curve for any point on the celestial sphere. We present the tool, describe its capabilities, limitations, and known issues, and provide a few illustrative examples.
1. INTRODUCTION
ASAS-SN extends all-sky variability surveying toward public, unbiased access by offering current light curves for arbitrary sky positions. Its first light-curve server provides real-time aperture photometry while establishing a staged path toward precomputed databases.
- Motivation and scope: ASAS-SN routinely surveys the entire visible sky to roughly 17 mag and offers a light curve for any user-selected sky position.The tool addresses the need for all-sky variability surveys and public access without restricting the requested location.
- Scientific context: The survey has focused primarily on bright transients, substantially increasing bright-supernova discoveries while reducing the amateur-search bias toward large host galaxies.ASAS-SN also finds more supernovae near galaxy cores than other amateur and professional searches.
- Scientific context: ASAS-SN has routinely discovered diverse additional transients, including cataclysmic variables, novae, dwarf flares, young stellar-object outbursts, tidal disruption events, and changing-look AGN.Cataclysmic variables are numerous enough to be released through a separate webpage and CV Patrol.
- First public tool: The first server computes aperture-photometry light curves on demand for arbitrary positions, avoiding team-imposed source selection but making the service relatively slow and unsuitable for bulk requests.The computations are performed when requested rather than retrieved from a precomputed sample.
- Future development: ASAS-SN planned staged releases from the initial on-demand tool to a database of known and newly discovered variables, followed by a complete database of ASAS-SN source light curves.The staged approach was intended to support controlled development, testing, and debugging.
2. ASAS-SN LIGHT CURVES
The ASAS-SN light-curve server computes aperture-photometry light curves on demand for arbitrary sky coordinates, while illustrating useful applications and important limits from coverage, crowding, and saturation.
- Tool and data processing: Because arbitrary positions are allowed, each requested light curve is computed at request time, making the tool slower than precomputed catalogs and unsuitable for bulk requests.The design avoids restricting users to a predefined source sample.
- Tool and data processing: The server accepts coordinates and a look-back time, returning a graph and downloadable table from aperture photometry on individual ASAS-SN images.Poor-quality, poorly focused, poorly astrometrized, and near-edge images are automatically rejected.
- Tool and data processing: Aperture photometry uses a 2-pixel-radius aperture, a 7–10-pixel background annulus, and calibration against 100 nearby APASS stars.Background pixels are clipped at 2σ.
- Illustrative examples: The examples show recovery of large-amplitude variability, 0.3 mag eclipses in a 1.11-day binary, and variability in a Small Magellanic Cloud star.The R CrB light curve spans 7.3 mag and remains well defined at its brightest points.
- Known issues: Crowding can alter flux and underestimate eclipse depths, although the period and eclipsing-binary nature remain recognizable in the WR20a example.The reported eclipse depth is about 0.3 mag instead of 0.4 mag.
- Known issues: ASAS-SN saturates at 10–11 mag, but its bleed-trail correction can substantially improve photometry of bright, relatively isolated saturated stars.The correction does not salvage stars beneath bleed trails, and the resulting photometry is unsuitable for determining the distance scale in the illustrated case.
3. DISCUSSION
V1.0 provides on-demand ASAS-SN light curves for any celestial coordinate, but real-time computation makes the service slow and unsuitable for large samples. Examples demonstrate useful coverage alongside issues from crowding, blending, saturation, and anomalous measurements.
- 3. DISCUSSION: Any celestial coordinate can yield an up-to-date ASAS-SN light curve on demand, making V1.0 an unprecedented all-sky resource.The service is most current for positions that are presently visible.
- 3. DISCUSSION: The examples include light curves for R Coronae Borealis, KELT J041621−620046, HV 2112, NGC 5548, and WR20a.The figures illustrate diverse variable and active sources, with data from different cameras shown in different colors.
- 3. DISCUSSION: Crowding and blending can distort ASAS-SN measurements, with WR20a eclipse depths underestimated by about 0.1 mag.Local crowding generally changes the light curve by an additive flux constant and reduces the observed eclipse amplitude.
- 3. DISCUSSION: 10, 33, 90, and 130 sec were required for look-back intervals of 20, 100, 1000 days, and the full data set, respectively.Recent-behavior requests are faster than full-light-curve requests.
- 3. DISCUSSION: The next planned phase will pre-compute light curves for known and newly discovered variables, improving speed but restricting coverage to a particular catalog.The broader scope of a later general-source phase remains undetermined.