ENTROPY DR1. High-resolution near-UV/optical spectra of 2MASS J11151597+1937266

ENTROPY Data Release 1 (v2.0)

Summary

The files in this data release consist of the flux-calibrated, stacked 1D spectum of the isolated, free-floating accreting planetary-mass object 2MASS J11151597+1937266 (2M1115). The data results from the high-resolution (R~50,000) observations by the Ultraviolet and Visual Echelle Spectrograph (UVES) at ESO's Very Large Telescope (VLT) in Chile, between 10-11 June 2023, taken as part of the ESO programme 0111.C-0166(A). This is the underlying data used for the analysis in the publication Viswanath et al. (2024) 

Details of Observations

The observations of 2M1115 with UVES were carried out between 10-11 June 2023 (MJD 60105, 60106) as part of the ExoplaNeT accretion mOnitoring sPectroscopic surveY (ENTROPY) in #Dichroic 1 mode with both the blue (390 nm) and red (580 nm) arms using a 0.8 arcsec wide slit without AO or chopping.

A total of four frames at 740 s exposure (NDIT=1) each were obtained across the two nights, giving a total integration time of 0.82 hr at an average seeing of 1.43 arcsec and an average airmass 1.416. The total wavelength range covered by the spectrum is 320–680 nm.

Target

Identifier: 2MASS J11151597+1937266

ICRS RA (ep=2016.0): 168.816234 deg

ICRA DEC (ep=2016.0): +19.623939 deg

Distance: 45.21 +- 2.20 pc

Age: 5-45 Myr

Mass: 6(+8, -4) Mjup

Radius: 1.5 +- 0.1 Rjup

Effective Temperature: 1816 +- 63 K

Data reduction

Each of the 4 raw data frames from the original set of exposures from the 2 nights were bias subtracted and flat-field corrected using the calibration files from ESO. Inter-order background was also subtracted. Cosmic rays were accounted for by using a horizontal median filtering and masking out pixels higher than 10 times the local variance. The flux was extracted order by order using standard aperture photometry, which included the subtraction of sky background and telluric lines.

The flux was calibrated based on the observations of a standard star taken contemporaneously with the same observing setup as the target, and was corrected for the relative slit loss (~4%) from seeing. Wavelength calibration was performed using the arc lamp spectrum and a Th–Ar line list. The wavelengths listed in the spectrum are in air. A barycentric velocity correction was applied to the wavelength calibration to transform the spectral reference system to that of the source. The stacked 1D spectrum available in this data release is obtained by taking the weighted average of the 4 individual spectra, with the weights determined from the respective photon noise.

Description of files

The data release in this second version consists of:

a) 1 merged spectrum UVES-2023.06.10-11.2M1115.merged-spectra.txt covering the entire UVES range of these observations (320–680 nm). The flux for the overlapping wavelengths in adjacent orders of each arm were averaged to get a single flux value per wavelength. This allows for easy access of the entire spectral range of all arms together. The ASCII file has 4 columns:

Column1 : Wavelength, in ångstrøm

Column2 : Flux, in units ergs/s/cm2/ångstrøm

Column3 : Flux_stddev, the weighted standard deviation of the flux across the 4 individual spectra, in units of ergs/s/cm2/ångstrøm (This is the recommended error bar)

Column4 : Flux_phot_err, Average of the photometric uncertainties in flux across the 4 spectra, in units of ergs/s/cm2/ångstrøm

b) The compressed file UVES-2023.06.10-11.2M1115.non-merged-spectra.zip contains one folder per each of the three arms (Blue, RedL, RedU). The folders include ASCII files containing the spectrum for individual orders of each arm, provided for the purpose of preserving the signal-to-noise ratio (S/N) of all orders. Some important emission lines like H𝛽 occur in both adjacent orders but at different signal strengths. Merging the orders by averaging the flux as in file (a) will suppress the S/N of such emission lines.

The order numbers of the respective arms containing detected emission lines from 2M1115 can be found in Tables 2 and G.1 in Viswanath et al. (2024). For the following Balmer lines detected in Viswanath et al. (2024), the corresponding rest wavelengths appear in two consecutive orders as indicated below:

Line
Arm
Orders
Detection in Viswanath et al. (2024)

H𝛽
RedL
2, 3
Both at > 3σ S/N 

Hγ
Blue
34, 35
Both at > 3σ S/N 

Hδ
Blue
28, 29
Only in 28

H7
Blue
24, 25 
Both, but only ~2σ S/N in 24

H9
Blue
20, 21
At only ~2σ S/N in both

Each ASCII file has 4 columns with same description as in file (a). To plot the spectrum of all the orders of all the arms, the following python code can be used:

import numpy as npfrom glob import globfrom natsort import natsortedarms = ['BLUE', 'REDL', 'REDU']plt.figure()for arm in arms:    files = natsorted(glob(f'UVES-2023.06.10-11.2M1115.non-merged-spectra/{arm}/*.txt'))    print(files)    for i in range(len(files)):        data = np.loadtxt(files[i])        plt.plot(data[:, 0], data[:, 1])plt.show()

c) 2M1115-Photometry.txt, an ASCII file containing the existing photometry for the target

Changes from previous version V1.0

The merged spectrum UVES-2023.06.10-11.2M1115.merged-spectra.txt in this version has been modified to preserve the original spectral resolution in the overlapping wavelegth regions. In V1.0, the corresponding regions had double the resolution due to an error in the interpolation method used.

The non-merged spectra of the individual orders have been replaced in this version as a compressed zip folder (instead of .npz files) containing ASCII files for spectra of each individual order to facilitate easier data handling.

The photometry file has been updated from that of last version with more information, including two additional filter bands (Gaia Gbp and Grp) as well as effective filter widths of all provided filter bands.