129 research outputs found
Zwicky Transient Facility and Globular Clusters: Calibration of the gr-Band Absolute Magnitudes for the Yellow Post-Asymptotic-Giant-Branch Stars
We present the first absolute calibration for the yellow
post-asymptotic-giant-branch (PAGB) stars in the g- and r-band based on
time-series observations from the Zwicky Transient Facility. These absolute
magnitudes were calibrated using four yellow PAGB stars (one non-varying star
and three Type II Cepheids) located in the globular clusters. We provide two
calibrations of the gr-band absolute magnitudes for the yellow PAGB stars, by
using an arithmetic mean and a linear regression. We demonstrate that the
linear regression provides a better fit to the g-band absolute magnitudes for
the yellow PAGB stars. These calibrated gr-band absolute magnitudes have a
potential to be used as population II distance indicators in the era of
time-domain synoptic sky surveys.Comment: 6 pages, 3 Figures and 1 Table; AJ accepte
Zwicky Transient Facility and Globular Clusters: the gr-Band Period-Luminosity Relations for Mira Variables at Maximum Light and Their Applications to Local Galaxies
Based on 14 Miras located in 7 globular clusters, we derived the first
gr-band period-luminosity (PL) at maximum light for the large-amplitude Mira
variables using the multi-year light-curve data collected from the Zwicky
Transient Facility (ZTF). Since Miras are red variables, we applied a
color-term correction to subsets of ZTF light curves, and found that such
corrections do not have a large impact on period determinations. We applied our
derived PL relations to the known extragalactic Miras in five local galaxies
(Sextans, Leo I, Leo II, NGC6822 and IC1613), and determined their Mira-based
distances. We demonstrated that our PL relations can be applied to short-period
(<300 days) Miras, including those in the two most distant galaxies (NGC6822
and IC1613) in our sample even when only a portion of the light-curves around
maximum light have detections. We have also shown that the long-period
extragalactic Miras do not follow the PL relations extrapolated to longer
periods. Hence, our derived PL relations are only applicable to the
short-period Miras, which will be discovered in abundance in local galaxies
within the era of Vera C. Rubin Observatory's Legacy Survey of Space and Time.Comment: 12 pages, 2 Tables and 10 Figures, AJ accepte
The Zwicky Transient Facility Alert Distribution System
The Zwicky Transient Facility (ZTF) survey generates real-time alerts for
optical transients, variables, and moving objects discovered in its wide-field
survey. We describe the ZTF alert stream distribution and processing
(filtering) system. The system uses existing open-source technologies developed
in industry: Kafka, a real-time streaming platform, and Avro, a binary
serialization format. The technologies used in this system provide a number of
advantages for the ZTF use case, including (1) built-in replication,
scalability, and stream rewind for the distribution mechanism; (2) structured
messages with strictly enforced schemas and dynamic typing for fast parsing;
and (3) a Python-based stream processing interface that is similar to batch for
a familiar and user-friendly plug-in filter system, all in a modular, primarily
containerized system. The production deployment has successfully supported
streaming up to 1.2 million alerts or roughly 70 GB of data per night, with
each alert available to a consumer within about 10 s of alert candidate
production. Data transfer rates of about 80,000 alerts/minute have been
observed. In this paper, we discuss this alert distribution and processing
system, the design motivations for the technology choices for the framework,
performance in production, and how this system may be generally suitable for
other alert stream use cases, including the upcoming Large Synoptic Survey
Telescope.Comment: Published in PASP Focus Issue on the Zwicky Transient Facility (doi:
10.1088/1538-3873/aae904). 9 Pages, 2 Figure
A Search for Extra-Tidal RR Lyrae in the Globular Cluster NGC 5024 and NGC 5053
Recently, Kundu et al (2019) reported that the globular cluster NGC 5024 (M53) possesses five extra-tidal RR Lyrae. In fact, four of them were instead known members of a nearby globular cluster NGC 5053. The status of the remaining extra-tidal RR Lyrae is controversial depending on the adopted tidal radius of NGC 5024. We have also searched for additional extra-tidal RR Lyrae within an area of ∼8~deg² covering both globular clusters. This includes other known RR Lyrae within the search area, as well as stars that fall within the expected range of magnitudes and colors for RR Lyrae (and yet outside the cutoff of 2/3 of the tidal radii of each globular clusters for something to be called "extra-tidal") if they were extra-tidal RR Lyrae candidates for NGC 5024 or NGC 5053. Based on the the proper motion information and their locations on the color-magnitude diagram, none of the known RR Lyrae belong to the extra-tidal RR Lyrae of either globular clusters. In the cases where the stars satisfied the magnitude and color ranges of RR Lyrae, analysis of time series data taken from the Zwicky Transient Facility do not reveal periodicities, suggesting that none of these stars are RR Lyrae. We conclude that there are no extra-tidal RR Lyrae associated with either NGC 5024 or NGC 5053 located within our search area
First results from the Very Small Array -- I. Observational methods
The Very Small Array (VSA) is a synthesis telescope designed to image faint
structures in the cosmic microwave background on degree and sub-degree angular
scales. The VSA has key differences from other CMB interferometers with the
result that different systematic errors are expected. We have tested the
operation of the VSA with a variety of blank-field and calibrator observations
and cross-checked its calibration scale against independent measurements. We
find that systematic effects can be suppressed below the thermal noise level in
long observations; the overall calibration accuracy of the flux density scale
is 3.5 percent and is limited by the external absolute calibration scale.Comment: 9 pages, 10 figures, MNRAS in press (Minor revisions
Towards Efficient Detection of Small Near-Earth Asteroids Using the Zwicky Transient Facility (ZTF)
We describe ZStreak, a semi-real-time pipeline specialized in detecting
small, fast-moving near-Earth asteroids (NEAs) that is currently operating on
the data from the newly-commissioned Zwicky Transient Facility (ZTF) survey.
Based on a prototype originally developed by Waszczak et al. (2017) for the
Palomar Transient Factory (PTF), the predecessor of ZTF, ZStreak features an
improved machine-learning model that can cope with the data rate
increment between PTF and ZTF. Since its first discovery on 2018 February 5
(2018 CL), ZTF/ZStreak has discovered confirmed new NEAs over a total of
232 observable nights until 2018 December 31. Most of the discoveries are small
NEAs, with diameters less than m. By analyzing the discovery
circumstances, we find that objects having the first to last detection time
interval under 2 hr are at risk of being lost. We will further improve
real-time follow-up capabilities, and work on suppressing false positives using
deep learning.Comment: PASP in pres
A New Class of Changing-Look LINERs
We report the discovery of six active galactic nuclei (AGN) caught "turning
on" during the first nine months of the Zwicky Transient Facility (ZTF) survey.
The host galaxies were classified as LINERs by weak narrow forbidden line
emission in their archival SDSS spectra, and detected by ZTF as nuclear
transients. In five of the cases, we found via follow-up spectroscopy that they
had transformed into broad-line AGN, reminiscent of the changing-look LINER
iPTF 16bco. In one case, ZTF18aajupnt/AT2018dyk, follow-up HST UV and
ground-based optical spectra revealed the transformation into a narrow-line
Seyfert 1 (NLS1) with strong [Fe VII, X, XIV] and He II 4686 coronal lines.
Swift monitoring observations of this source reveal bright UV emission that
tracks the optical flare, accompanied by a luminous soft X-ray flare that peaks
~60 days later. Spitzer follow-up observations also detect a luminous
mid-infrared flare implying a large covering fraction of dust. Archival light
curves of the entire sample from CRTS, ATLAS, and ASAS-SN constrain the onset
of the optical nuclear flaring from a prolonged quiescent state. Here we
present the systematic selection and follow-up of this new class of
changing-look LINERs, compare their properties to previously reported
changing-look Seyfert galaxies, and conclude that they are a unique class of
transients well-suited to test the uncertain physical processes associated with
the LINER accretion state.Comment: Submitted to ApJ, 31 pages, 17 Figures (excluding Appendix due to
file size constraints but will be available in electronic version
- …