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astro-ph.SR · Solar and Stellar Astrophysicsastro-ph.EP · Earth and Planetary Astrophysics

Fewer than 10 % of Gaia DR3 SB1 orbits with m2min < 0.08 Msun are real: TESS shows 14 transits where 404 are expected (P ≤ 16 d) and 65 ellipsoidal signals where 922 are expected (r = 1)

Gaia DR3 gives 3,740 single-lined spectroscopic (SB1) orbits with a minimum companion mass m2min < 0.08 Msun, P = 0.5-60 d and a main-sequence primary (G < 14). If these orbits are real, they put many brown dwarfs into the brown-dwarf desert. We tested the orbits with TESS in two ways: (1) a box search at the Gaia period and phase for 3,666 stars, with injections, a control search at false periods, a shape test and timing checks; (2) a fit of the ellipsoidal variation at P/2 in PDCSAP flux for 1,662 stars, with a noise model from 30 control periods. A positive control of 44 TOIs with a Gaia SB1 orbit at the TOI period gave 44 of 44 transit detections. It also calibrated the ellipsoidal amplitude (c = 0.63, 68 %: 0.57-0.70). The ratio F of the observed and the expected number of signals is the fraction of real orbits. For a flat companion mass function (r = 1) and P ≤ 16 d, TESS shows 14 transit-like signals (4 control false alarms) where 404 are expected: F = 0.025 (95 % upper limit 0.047). The ellipsoidal test finds 65 signals (36 clean signals without a k = 1 excess) where 922 are expected: F = 0.07 (95 %: 0.087). The transit test depends strongly on r: for few substellar companions (r = 0.03), F can be 0.6. The ellipsoidal test does not: for r = 0.03 to 3, F = 0.064-0.097 and the 95 % upper limit is less than 0.12 (0.071 for the clean signals). For primaries with Teff ≤ 6000 K, we find 0 ellipsoidal signals where 335 are expected (F < 0.009, 95 %) and 1 transit where 140 are expected (P = 0.5-4 d). All the ellipsoidal signals are on hotter stars, which often pulsate or are eclipsing binaries. Their amplitudes are smaller than predicted (KS p = 8.5e-6). Thus F for the hot stars is an upper limit. Orbits with 0.08 ≤ m2min < 0.15 Msun give F = 0.30 (transits) and 0.37 (ellipsoidal). Thus the fraction of false orbits increases when m2min decreases. The QLP ellipsoidal test of sci:sha256:be44296e576666e16eee60eb46d7ed9988006cb8fa86ff89aef7a169b6946693 agrees: it rules out 94 % of the testable cool-star orbits at 0.5-1 d. We list 3 transit candidates at P ≤ 16 d and 6 at P > 16 d that have no TOI and no vetting flag. The supporting ZIP has the code, the TESS product lists and all results. We removed the Gaia DR3 values from it for licence reasons. A script adds them again.

Gaia DR3 · spectroscopic binaries · SB1 orbits · brown dwarfs · brown-dwarf desert · TESS · transits · ellipsoidal variation · BEER model · false orbits · orbit validation · box least squares · injection-recovery · low-mass companions · PDCSAP · QLP · non-single stars · population statistics · transiting brown dwarf candidates · stellar variability

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References

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  1. supportsTESS photometry shows that under 1% of Gaia DR3 SB1 orbits at 0.25-0.3 d and 2.6-6% at 0.3-0.5 d are real, for dwarf hosts, minimum companion mass below 0.15 Msun and ellipsoidal model scale 0.22-1 sci:sha256:be44296e576666e16eee60eb46d7ed9988006cb8fa86ff89aef7a169b6946693

    Their QLP ellipsoidal test finds that few Gaia DR3 SB1 orbits with m2min < 0.15 Msun are real. Our independent PDCSAP ellipsoidal test and TESS transit test give the same result for m2min < 0.08 Msun (F < 0.1) and F = 0.37 for 0.08-0.15 Msun. We use their verdict table for a star-by-star comparison (section 4.6). Our calibration with known transiting companions gives c = 0.63, and our results give possible causes of their scale of 0.35.

  2. supportsCatalog values for 2,668 Gaia DR3 SB1 entries with periods below 10 days fail a detached-star test under a periastron Roche model sci:sha256:8df05a84d11a9aa0d6da7b79e3a0663f5158596f8fd43b84e26fe40637edb9c0

    They found that 2,668 Gaia DR3 SB1 entries with P < 10 d fail a detached-star test. We find that fewer than 10 % of the SB1 orbits with m2min < 0.08 Msun and P <= 16 d are real.

  3. supportsGaia eclipse periods disagree with 32 of 39 SB1 entries flagged by a detached-star test in a 1,643-source sample sci:sha256:6ce1fde432bc3216b9e2a416e8b8e9b19a6fe0263e063e4bb571d6a9792b2347

    They found that Gaia eclipse periods disagree with most flagged SB1 entries. Our transit and ellipsoidal tests also show that most short-period SB1 orbits in the brown-dwarf mass range are false.

  4. usesGaia DR3 SB1 orbits predict eclipse times with errors 1.45 times too small and 2.8% gross outliers, in a test with 1582 Gaia and 416 TESS eclipsing binaries of period mostly below 10 d sci:sha256:dd865fb0fe9055c98a3460d9be2bbf502e8b89f6a76ac3e6eb991affe46753d7

    Their result (Gaia eclipse-time errors 1.45 times too small, 2.8 % gross outliers) sets our off-phase flag: it needs both a 3-sigma time offset and a phase offset of more than 0.1.

  5. Valid Gaia DR3 SB1 orbits require companions above 0.08 solar masses for TOI-6936.01 and TOI-7590.01 sci:sha256:0c7eca695c8dfeb93628168c5be26fd92961d46b9439ba01ab1aaaacd41fdcf9

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