UKIRT Microlensing Survey Information

Here we present the publicly available data for the UKIRT microlensing survey. These light curves were acquired from 2015 to 2019 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 inner 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.

2017 marked the first year of the dedicated WFIRST precursor survey, for which the observing program changed to focus on the central Galactic bulge, include K-band observations, and implement a tiered observing strategy. For each target field, the primary and secondary survey filter as well as the observing cadence was determined by the on-sky location (see the UKIRT Coverage Maps and Magnitude Ranges page for more details). The 2017 UKIRT microlensing survey thus observed in both H- and K-band over 131 nights, spanning reduced HJD = 7864–7994 and covering 10.5 deg2. The 2018 UKIRT microlensing survey also observed in both H- and K-band over 116 nights, spanning reduced HJD = 8223–8337. We note there was significant weather loss between 8225–8254 and that only a few epochs of baseline data were obtained for the northern Galactic Bulge Region fields during the 2018 survey.

Finally, 2019 marked the final year of the UKIRT microlensing survey, which observed both H- and K-band over 146 nights, spanning reduced HJD = 8590-8736

Exoplanet Archive UKIRT Resources

The NASA Exoplanet Archive hosts 100.5 million UKIRT light curves, totaling ? GB of data. Here is the breakdown of the data volume by survey year and filter:

Year and Band Number of Light Curves [million] Data [GB]
2015 (H-band) 6.7 26.4
2016 (H-band) 11.3 48.6
2017 (H-band) 17.3 31.8
2017 (K-band) 17.0 52.0
2018 (H-band) 14.9 17.5
2018 (K-band) 11.0 27.9
2019 (H-band) 10.9 16.3
2019 (K-band) 11.5 43.5
Total (2015–2019; H- and K-band) 100.5 263

In total, this data volume is 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) Table Access Protocol (TAP) Access Data Column Defintions (for TAP queries)
UKIRT Light Curves Search Interface

Additional Documents

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, 2015–2019
  • Galactic Bulge Region (cf. Observational Coverage Maps):
    • 'c' for the central Galactic bulge fields from the 2017–2019 UKIRT microlensing surveys
    • '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 2017–2019 UKIRT microlensing surveys
    • '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 2017–2019 UKIRT microlensing surveys
  • 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 Coverage Maps and Magnitude Ranges 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 2015–2019 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: 2015–2019) is within 0.6" of a given UKIRT source (in that same year), it is identified as a match.
  • If an OGLE or MOA microlensing event is within 2" of a UKIRT microlensing event in the same year, the two events are considered a match—even if the positional difference is greater than 0.6".
  • 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.

If a given OGLE or MOA microlensing event is >0.6" from a UKIRT source, and the UKIRT source was not identified (and is missing) 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

In addition to the language provided on this page, please include the following Digital Object Identifier (DOI) as part of your acknowledgment:

DOI 10.26133/NEA7

See the full list of NASA Exoplanet Archive DOIs for other data sets and services.

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.

2018 - 2019: 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. The collection of the 2018 data reported here was supported by NASA grant NNG16PJ32C and JPL proposal #18-NUP2018-0016.

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: 1 March 2022