J/AJ/156/178 NIR transmission spectra of TRAPPIST-1 planets (Zhang+, 2018) ================================================================================ The near-infrared transmission spectra of TRAPPIST-1 planets b, c, d, e, f, and g and stellar contamination in multi-epoch transit spectra. Zhang Z., Zhou Y., Rackham B.V., Apai D. =2018AJ....156..178Z (SIMBAD/NED BibCode) ================================================================================ ADC_Keywords: Exoplanets ; Effective temperatures ; Spectra, infrared ; Stars, double and multiple Keywords: planets and satellites: atmospheres - planets and satellites: individual TRAPPIST-1 - planets and satellites: terrestrial planets - stars: late-type - techniques: spectroscopic Abstract: The seven approximately Earth-sized transiting planets in the TRAPPIST-1 system provide a unique opportunity to explore habitable- and nonhabitable-zone small planets within the same system. Its habitable-zone exoplanets - due to their favorable transit depths - are also worlds for which atmospheric transmission spectroscopy is within reach with the Hubble Space Telescope (HST) and James Webb Space Telescope (JWST). We present here an independent reduction and analysis of two HST Wide Field Camera 3 (WFC3) near-infrared transit spectroscopy data sets for six planets (b through g). Utilizing our physically motivated detector charge-trap correction and a custom cosmic-ray correction routine, we confirm the general shape of the transmission spectra presented by de Wit et al. (2016Natur.537...69D). Our data reduction approach leads to a 25% increase in the usable data and reduces the risk of confusing astrophysical brightness variations (e.g., flares) with instrumental systematics. No prominent absorption features are detected in any individual planet's transmission spectra; by contrast, the combined spectrum of the planets shows a suggestive decrease around 1.4 {mu}m similar to an inverted water absorption feature. Including transit depths from K2, the SPECULOOS-South Observatory, and Spitzer, we find that the complete transmission spectrum is fully consistent with stellar contamination owing to the transit light source effect. These spectra demonstrate how stellar contamination can overwhelm planetary absorption features in low-resolution exoplanet transit spectra obtained by HST and JWST and also highlight the challenges in combining multi-epoch observations for planets around rapidly rotating spotted stars. Description: The data presented in this study were obtained in two HST Wide Field Camera 3 (WFC3) programs (GO-14500 and GO-14873, PI: de Wit) targeting the TRAPPIST-1 system. In the following, we refer to the two programs as Program 1 and Program 2, respectively. Program 1 consists of one visit, executed on 2016 May 4, and covers the overlapping transits of planets TRAPPIST-1 b and c. The results were initially published in de Wit et al. (2016Natur.537...69D). Program 2 consists of four visits, executed between 2016 December and 2017 January, and covers the transits of planets TRAPPIST-1 d, e, f, and g (de Wit et al. 2018NatAs...2..214D). In the two programs, the six inner planets (TRAPPIST-1 b-g) have been observed at least once during transit. In addition, the observations include two overlapping transits of the planet pairs b and c and e and g. For convenience, we label the seven transits in chronological order as Transit 1, 2, 3, 4, 5, 6, and 7. Objects: --------------------------------------------------------- RA (ICRS) DE Designation(s) --------------------------------------------------------- 23 06 29.37 -05 02 29.0 TRAPPIST-1 = EPIC 246199087 --------------------------------------------------------- File Summary: -------------------------------------------------------------------------------- FileName Lrecl Records Explanations -------------------------------------------------------------------------------- ReadMe 80 . This file table5.dat 36 6 Parameters used as input in transit profile fitting from Gillon et al. (2016Natur.533..221G, 2017Natur.542..456G) table8.dat 70 7 Planetary parameters for water absorption calculations table13.dat 33 84 Transmission spectra table14.dat 33 77 Transmission spectra in the interpolated bins -------------------------------------------------------------------------------- See also: J/A+A/549/A10 : Transits of GJ 1214 (Harpsoe+, 2013) J/A+A/563/A21 : GJ 1214 Trappist and Spitzer light curves (Gillon+, 2014) J/ApJ/799/180 : Radii of 430 KOI Earth- to Neptune-sized planets (Silburt+, 2015) Byte-by-byte Description of file: table5.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1 A1 --- Pl [bcdefg] TRAPPIST-1 planet 3- 8 F6.3 deg Incl [89.65/89.86] Inclination (1) 10- 14 F5.3 deg E_Incl [0.025/0.22] Upper limit uncertainty in Incl 16- 20 F5.3 deg e_Incl [0.025/0.27] Lower limit uncertainty in Incl 22- 30 F9.6 d T [1.5109/12.35294] Orbital period (2) 32- 36 F5.2 --- a [20.5/83.2] Semimajor axis, expressed in units of stellar radius -------------------------------------------------------------------------------- Note (1): Gaussian-distributed priors. Note (2): Fixed parameters. -------------------------------------------------------------------------------- Byte-by-byte Description of file: table8.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1 A1 --- Pl [bcdefg] TRAPPIST-1 planet 3- 7 F5.3 Mgeo Mass [0.24/1.63] Planet mass 9- 14 F6.4 Mgeo E_Mass [0.0038/0.63] Uperr limit uncertainty in Mass 16- 21 F6.4 Mgeo e_Mass [0.0038/0.63] Lower limit uncertainty in Mass 23- 27 F5.1 K Teff [198.6/400.1] Effective temperature 29- 31 F3.1 K e_Teff [3.8/7.7] Uncertainty in Teff 33- 36 I4 ppm Deltad [-413/77] Transit depth {Delta}d 38- 40 I3 ppm e_Deltad [113/266] Uncertainty in Deltad 42- 46 F5.3 Rgeo Rad [0.772/1.127] Planet radius 48- 52 F5.3 Rgeo e_Rad [0.03/0.041] Uncertainty in Rad 54- 58 F5.1 --- AH [-11.1/2.5] Water absorption amplitude A_H_ (see Equation (5)) 60- 63 F4.1 --- e_AH [1/13.6] Uncertainty in AH 65- 68 F4.1 --- E_AH [3.2/29.7] 3{sigma} upper bound of AH 70 I1 --- Trans [1/7] Transit number -------------------------------------------------------------------------------- Byte-by-byte Description of file: table13.dat table14.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1 I1 --- Trans [1/7] Transit number 3 A1 --- Pl [bcdefg] TRAPPIST-1 planet 5- 9 I5 0.1nm Wave [11377/16613]? Wavelength ({AA}) (only in Table 13) (1) 11- 17 F7.5 --- Depth [0.00356/0.00824] Transit depth 19- 25 F7.5 --- E_Depth [9e-05/0.00037] Upper limit uncertainty in Depth 27- 33 F7.5 --- e_Depth [9e-05/0.00038] Lower limit uncertainty in Depth -------------------------------------------------------------------------------- Note (1): In Table 14, the central wavelengths of the 11 bins are an arithmetic series from 11500 to 16500 {AA}. -------------------------------------------------------------------------------- History: From electronic version of the journal ================================================================================ (End) Tiphaine Pouvreau [CDS] 21-Mar-2019