UKIRT Microlensing Survey Information

Here we present the first public data release for the ongoing UKIRT microlensing survey. These light curves were acquired from 2015 to 2016 and have been made available to the public via the NASA Exoplanet Archive, with help from the UKIRT Microlensing Team.

UKIRT Microlensing Survey

The Wide Field Camera (WFCAM) on the United Kingdom Infrared Telescope (UKIRT), located at Mauna Kea Observatory, has been used in recent years to conduct microlensing surveys with a variety of science goals. These goals include providing simultaneous near-infrared (NIR) observational coverage of ongoing ground- and space-based microlensing surveys, which will facilitate later direct measurements (or constraints) of the flux from the lensing systems, and empirically measure, for the first time, the NIR microlensing event rate toward the center of the Milky Way.

In 2015, WFCAM on UKIRT was first used to conduct a microlensing survey of the central Galactic bulge, specifically in support of a space-based microlensing campaign using the Spitzer Space Telescope. The 2015 UKIRT microlensing survey observed in H-band for 120 hours over 39 nights, spanning reduced HJD (HJD - 2450000) = 7180–7219 and covering 3.4 deg2, with a nominal cadence of 5 epochs per night. This was subsequently followed by a 2016 UKIRT campaign, again using WFCAM, to provide simultaneous NIR coverage of the K2 Campaign 9 (K2C9) survey superstamp area. The 2016 UKIRT microlensing survey observed in H-band for 240 hours over 91 nights, spanning reduced HJD = 71807219 and covering 6.0 deg2, with a nominal cadence of 2–3 epochs per night.

Exoplanet Archive UKIRT Resources

The NASA Exoplanet Archive hosts 17.95 million UKIRT light curves, totaling 75.00 gigabytes (GB) of data. In total, this is far too large to view or download through a web browser. Please see the links below to search through or download these data.

  Interactive Tables (Also see: How to use interactive tables) API Query Documentation
UKIRT Light Curves Search Interface

UKIRT Source ID Naming Convention

Each UKIRT light curve source ID follows the same format:

'ukirt' + '_' + <Photometry Method> + '_' + <Survey Year> + '_' + <Galactic Bulge Region> + '_' + <Field ID> + '_' + <CCD ID> + '_' + <Index>
  • ukirt: identifies that we are publishing UKIRT photometry products
  • Photometry Method: the c identifies that this specific photometry product was produced by the CASU pipeline
  • Survey Year: identifies the survey year, either 2015 or 2016
  • Galactic Bulge Region (cf. Observational Coverage Maps):
    • 'n' for UKIRT fields with a positive (northern) Galactic latitude b, corresponding to the 2015 UKIRT microlensing survey
    • 's' for UKIRT fields with a negative (southern) Galactic latitude b, corresponding to the 2016 UKIRT microlensing survey
  • Field ID and CCD ID:
    • The WFCAM focal plane consists of four non-overlapping CCDs arranged in a square 40.13' on a side, for which the separation between CCDs is 94% of a CCD dimension. Here we refer to each 4-CCD pointing as a "field," and each CCD within a given field is identified via "CCD." Given that four fields can thus be organized to create a contiguous observational square, with no gaps (and some overlap, given the aforementioned CCD separation), we organize fields in groups of four. For example, the first four fields are labeled 11, 12, 13, 14; the second four are labeled 21, 22, 23, and 24, etc.
    • The two exceptions to this are the two fields with the most positive Galactic latitude b in the 2015 data (see the UKIRT Microlensing Survey Figures page), which are simply referred to as fields 5 and 6.
  • Index: a running seven-digit integer that uniquely identifies a given UKIRT source: located on a given CCD of a given field, within a survey field for a given survey year, extracted using a given photometric pipeline

For example, the 2016 UKIRT source with ID 65104 on CCD 1 within field 33 has the name:


UKIRT Matching to OGLE and MOA Microlensing Surveys

We have cross-matched each of the 2015 and 2016 UKIRT survey databases to both the Optical Gravitational Lensing Experiment (OGLE) microlensing survey Early Warning System (EWS) event page and the Microlensing Observations in Astrophysics (MOA) Transient Alert event page for the corresponding survey year. The matching criteria are as follows:

  • If a given OGLE or MOA microlensing event (in a given year: 2015 or 2016) is within 0.6" of a given UKIRT source (in that same year), it is identified as a match.
  • If a given OGLE or MOA microlensing event (in a given year) matches to a UKIRT source (in that same year) that has been identified by the UKIRT Microlensing Team event detection pipeline to have significant flux variation but is >0.6" away, it is identified as a match. In all cases, the match is yet within 2–3".
  • If a given microlensing event (in a given year) is identified separately by both OGLE and MOA but only one is within 0.6" of a UKIRT source (in that same year), then both the OGLE and MOA microlensing events are identified as a match.

Given that the UKIRT Microlensing Team event detection pipeline is yet under development, a final "by-eye" approach was undertaken. Specifically, if a given OGLE or MOA microlensing event is >0.6" from a UKIRT source, the UKIRT source was not identified as a UKIRT microlensing event, but upon visual inspection the UKIRT light curve displays a clear microlensing signal at the expected time given by the OGLE or MOA microlensing event light curve, this is included as a match. As a result of this process, 9 additional events were included as matches:

  • OGLE-2015-BLG-1641: ukirt_c_2015_n_21_2_0065466
  • OGLE-2016-BLG-0767: ukirt_c_2016_s_61_3_0049492
  • OGLE-2016-BLG-0863: ukirt_c_2016_s_54_4_0077414
  • OGLE-2016-BLG-0981: ukirt_c_2016_s_11_4_0021566
  • OGLE-2016-BLG-0989: ukirt_c_2016_s_72_4_0025617
  • MOA-2016-BLG-123: ukirt_c_2016_s_54_1_0032070
  • MOA-2016-BLG-227: ukirt_c_2016_s_22_2_0063572
  • MOA-2016-BLG-296: ukirt_c_2016_s_51_2_0081542
  • MOA-2016-BLG-392: ukirt_c_2016_s_23_2_0076905

Finally, we note that OGLE and MOA data may not be reproduced or published without the explicit permission of the corresponding survey team! Please refer to the links above (or the bubble link, for a given UKIRT event with an OGLE and/or MOA match) to find the appropriate contact information.

Requested Data Acknowledgements

UKIRT General Data Acknowledgement

UKIRT is owned by the University of Hawaii (UH) and operated by the UH Institute for Astronomy; operations are enabled through the cooperation of the East Asian Observatory. When the 20152016 data reported here were acquired, UKIRT was supported by NASA and operated under an agreement among the University of Hawaii, the University of Arizona, and Lockheed Martin Advanced Technology Center; operations were enabled through the cooperation of the East Asian Observatory.

UKIRT 2016 Data Additional Acknowledgement

We acknowledge the support from NASA HQ for the UKIRT observations in connection with K2C9.

NASA Exoplanet Archive Acknowledgement

This paper makes use of data from the UKIRT microlensing surveys (Shvartzvald et al. 2017) provided by the UKIRT Microlensing Team and services at the NASA Exoplanet Archive, which is operated by the California Institute of Technology, under contract with the National Aeronautics and Space Administration under the Exoplanet Exploration Program.

Mauna Kea Cultural Acknowledgement

The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to use data produced from observations conducted on this mountain.

Additional Project Resources

Last updated: 8 December 2017