Achieving Better Than 1 Minute Accuracy in the Heliocentric and Barycentric Julian Dates

By Jason Eastman, R. Siverd, B. Gaudi. 2010

666 citations recorded by the source corpus.

As the quality and quantity of astrophysical data continue to improve, the precision with which certain astrophysical events can be timed becomes limited not by the data themselves, but by the manner, standard, and uniformity with which time itself is referenced. While some areas of astronomy (most notably pulsar studies) have required absolute time stamps with precisions of considerably better than 1 minute for many decades, recently new areas have crossed into this regime. In particular, in the exoplanet community, we have found that the (typically unspecified) time standards adopted by various groups can differ by as much as a minute. Left uncorrected, this ambiguity may be mistaken for transit timing variations and bias eccentricity measurements. We argue that, since the commonly-used Julian Date, as well as its heliocentric and barycentric counterparts, can be specified in several time standards, it is imperative that their time standards always be reported when accuracies of 1 minute are required. We summarize the rationale behind our recommendation to quote the site arrival time, in addition to using BJDTDB, the Barycentric Julian Date in the Barycentric Dynamical Time standard for any astrophysical event. The BJDTDB is the most practical absolute time stamp for extraterrestrial phenomena, and is ultimately limited by the properties of the target system. We compile a general summary of factors that must be considered in order to achieve timing precisions ranging from 15 minutes to 1 µs. Finally, we provide software tools that, in principal, allow one to calculate BJDTDB to a precision of 1 μs for any target from anywhere on Earth or from any spacecraft.

Subfields: Astronomy and Astrophysics, Atomic and Molecular Physics, and Optics, Computational Mechanics

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Citations in the corpus

State of the Field: Extreme Precision Radial Velocities (2016, background): “An error of 1 second in time introduces a semiamplitude error of about 3 cm s−1, so to reach an error of less than 1 cm s−1 the midpoint time must be accurate to about 250 milli-seconds (Eastman et al. 2010; Wright & Eastman 2014).”
CHARACTERIZING THE COOL KOIs. II. THE M DWARF KOI-254 AND ITS HOT JUPITER (2011, methodology): “The Nickel and HIRES observation timestamps were converted to BJDUTC to match Kepler MAST data using the techniques of Eastman et al. (2010).”
THE KEPLER-10 PLANETARY SYSTEM REVISITED BY HARPS-N: A HOT ROCKY WORLD AND A SOLID NEPTUNE-MASS PLANET (2014, methodology): “For this purpose, the epochs of the HARPS-N observations were converted from BJDUTC into BJDTDB (Eastman et al. 2010), which is the time stamp of Kepler data.”
THE FLAT TRANSMISSION SPECTRUM OF THE SUPER-EARTH GJ1214b FROM WIDE FIELD CAMERA 3 ON THE HUBBLE SPACE TELESCOPE (2011, methodology): “We correct this to the mid-exposure time using the EXPTIME keyword, and convert it to the Barycentric Julian Date in the Barycentric Dynamical Time standard using the code provided by Eastman et al. (2010).”
Observations of Transiting Exoplanets with the James Webb Space Telescope (JWST) (2014, background): “TDB is a barycentric dynamical time and it is distinct from UTC in that it does not have leap seconds (Eastman et al. 2010).”
Barycentric Corrections at 1 cm s-1 for Precise Doppler Velocities (2014, background): “Such calculations are discussed in Eastman et al. (2010).”
HST hot-Jupiter transmission spectral survey: detection of potassium in WASP-31b along with a cloud deck and Rayleigh scattering (2014, methodology): “The mid-time of each exposure was converted into BJDTBD for use in the transit light curves (Eastman et al. 2010).”
The TRAPPIST survey of southern transiting planets. I. Thirty eclipses of the ultra-short period planet WASP-43 b (2012, methodology): “At the first step of the MCMC, the timings of the measurements are passed to theBJDT DB time standard, following the recommendation of Eastman et al. (2010) that outlined that the commonly-usedBJDUTC time standard is not practical for highprecision timing monitoring as it drifts with the addition…”
The Apparently Decaying Orbit of WASP-12b (2017, methodology): “The time stamps were placed on the BJDTDB system using the code of Eastman et al. (2010).”
HST hot-Jupiter transmission spectral survey: evidence for aerosols and lack of TiO in the atmosphere of WASP-12b (2013, methodology): “The mid-time of each exposure was converted into BJDTBD for use in the transit light curves (Eastman et al. 2010).”
KEPLER-18b, c, AND d: A SYSTEM OF THREE PLANETS CONFIRMED BY TRANSIT TIMING VARIATIONS, LIGHT CURVE VALIDATION, WARM-SPITZER PHOTOMETRY, AND RADIAL VELOCITY MEASUREMENTS (2011, methodology): “We convert to UTC-based BJD following the procedure developed by Eastman et al. (2010).”
3.6 AND 4.5 μm PHASE CURVES AND EVIDENCE FOR NON-EQUILIBRIUM CHEMISTRY IN THE ATMOSPHERE OF EXTRASOLAR PLANET HD 189733b (2012, methodology): “Eastman et al. (2010) further advocate a conversion from UTC to TT timing standards, which includes a more consistent treatment of leap seconds.”
THE CLIMATE OF HD 189733b FROM FOURTEEN TRANSITS AND ECLIPSES MEASURED BY SPITZER (2010, background): “…is important since heliocentric and barycentric Julian Date can differ by as much as a few seconds, and different time systems can vary by seconds depending on the number of leap seconds included, which is close to the timing precision we can achieve with these data (Eastman et al. 2010).”