UKIRT Microlensing Survey Information

Here we present the publicly available data for the ongoing UKIRT microlensing survey. These light curves were acquired from 2015 to 2017 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 events, which will facilitate later direct measurements (or constraints) of the flux from the lensing systems, and empirically measuring, 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 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 over 91 nights, spanning reduced HJD = 7487–7578 and covering 6.0 deg2, with a nominal cadence of 2–3 epochs per night.

The 2017 UKIRT microlensing survey observed in both H- and KS-band over 131 nights, spanning reduced HJD = 7864–7994 and covering 10.5 deg2, and featured a tiered observing strategy. For each target field, the primary and secondary survey filter, as well as the field determination, are determined by the on-sky location (see the UKIRT Microlensing Survey Figures page for more details).

Exoplanet Archive UKIRT Resources

The NASA Exoplanet Archive hosts 52.3 million UKIRT light curves, totaling 158.78 gigabytes (GB) of data. Here is the breakdown of the data volume by survey year and filter:

Year and Band Number of Light Curves Data (Gigabytes)
2015 (H-band) 6.7 million (6,699,459) 26.41
2016 (H-band) 11.3 million (11,257,251) 48.60
2017 (H-band) 17.3 million (17,260,355) 31.75
2017 (KS-band) 17.0 million (17,047,099) 52.02
Total (2015–2017; H- and KS-band) 52.3 million (52,264,168) 158.78

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, 2015–2017
  • Galactic Bulge Region (cf. Observational Coverage Maps):
    • 'c' for the central Galactic bulge fields from the 2017 UKIRT microlensing survey
    • 'n' for the northern Galactic bulge fields, i.e., all target fields from the 2015 UKIRT microlensing survey (all of which have positive Galactic latitude) as well as those designated as northern target fields from the 2017 UKIRT microlensing survey
    • 's' for the southern Galactic bulge fields, i.e., all target fields from the 2016 UKIRT microlensing survey (all of which have negative Galactic latitude) as well as those designated as southern target fields from the 2017 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_c_2016_s_33_1_0065104

UKIRT Matching to OGLE and MOA Microlensing Surveys

We have cross-matched each of the 2015–2017 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: 2015–2017) 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

2015: UKIRT is currently 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 2015 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.

2016: UKIRT is currently 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 2016 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. We furthermore acknowledge the support from NASA HQ for the UKIRT observations in connection with K2C9.

2017: UKIRT is currently 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 some of the 2017 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. The collection of the 2017 data reported here was furthermore partially supported by NASA grants NNX17AD73G and NNG16PJ32C.

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: 2 May 2018