J/A+A/688/A104 X-Shooting ULLYSES II. Data Release 1 (Sana+, 2024)
X-Shooting ULLYSES: Massive Stars at low metallicity.
II. DR1: Advanced optical data products for the Magellanic Clouds.
Sana H., Tramper F., Abdul-Masih M., Blomme R., Dsilva K., Maravelias G.,
Martins L., Mehner A., Wofford A., Banyard G., Barbosa C.L.,
Bestenlehner J., Hawcroft C., John Hillier D., Todt H., Larkin C.J.K.,
Mahy L., Najarro F., Ramachandran V., Ramirez-Tannus M.C., Rubio-Diez M.M.,
Sander A.A.C., Shenar T., Vink J.S., Backs F., Brands S.A., Crowther P.,
Decin L., de Koter A., Hamann W.-R., Kehrig C., Kuiper R., Oskinova L.,
Pauli D., Sundqvist J., Verhamme O., XSHOOT-U collaboration
<Astron. Astrophys. 688, A104 (2024)>
=2024A&A...688A.104S 2024A&A...688A.104S (SIMBAD/NED BibCode)
ADC_Keywords: Atlases ; Magellanic Clouds ; Spectroscopy ; Stars, O ;
Stars, OB ; Stars, B-type ; Stars, Wolf-Rayet
Keywords: techniques: spectroscopic - atlases - stars: early-type -
stars: massive - Magellanic Clouds
Abstract:
The XShootU project aims to obtain ground-based optical to
near-infrared spectroscopy of all targets observed by the Hubble Space
Telescope (HST) under the Director's Discretionary program ULLYSES.
Using the medium resolution spectrograph X-shooter, spectra of 235 OB
and Wolf-Rayet (WR) stars in sub-solar metallicity environments have
been secured. The bulk of the targets belong to the Large and Small
Magellanic Clouds, with the exception of three stars in NGC 3109 and
Sextans A.
This second paper of the series focuses on the optical observations of
Magellanic Clouds targets. It describes the uniform reduction of the
UVB (300-560nm) and VIS (550-1020nm) XShootU data as well as the
preparation of advanced data products that are suitable for
homogeneous scientific analyses.
The data reduction of the raw data is based on the ESO CPL X-shooter
pipeline. We paid particular attention to the determination of the
response curves. This required equal flat-fielding of the science and
flux standard star data and the derivation of improved flux standard
models. The pipeline products were then processed with our own set of
routines to produce a series of advanced data products. In particular,
we implemented slit-loss correction, absolute flux calibration,
(semi-)automatic rectification to the continuum, and a correction for
telluric lines. The spectra of individual epochs were further
corrected for the barycentric motion, re-sampled and co-added, and the
spectra from the two arms were merged into a single flux calibrated
spectrum covering the entire optical range with maximum
signal-to-noise ratio.
We identify and describe an undocumented recurrent ghost visible on
the raw data. We present an improved flat-fielding strategy that
limits artefacts when the science and flux standard stars are observed
on different nights. The improved flux standard models and the new
grid of anchor points allow to limit artefacts of the response curve
correction on, e.g., the shape of the wings of the Balmer lines, from
a couple of per cent of the continuum level to less than 0.5%. We
confirm the presence of a radial velocity shift of about 3.5km/s
between the UVB and the VIS arm of xshooter and that there is no short
term variations impacting the RV measurements. RV precision better
than 1km/s can be obtained on sharp telluric lines while RV precision
of the order of 2 to 3km/s are obtained on data with the best SNR.
For each target observed by XShootU, we provide three types of data
products: (i) two-dimensional spectra for each UVB and VIS exposure
before and after correction for the instrument response; (ii)
one-dimensional UVB and VIS spectra as produced by the X-shooter
pipeline before and after response-correction, as well as after
applying various processing, including absolute flux calibration,
telluric removal, normalisation and barycentric correction; and (iii)
co-added flux-calibrated and rectified spectra over the full optical
range, for which all available XShootU exposures were combined. For
the large majority of the targets, the final signal-to-noise ratio per
resolution element is above 200 in both the UVB and the VIS co-added
spectra. The reduced data and advanced scientific data products are
made available to the community. Together with the HST UV ULLYSES
data, they should enable various science goals, from detailed stellar
atmosphere and stellar wind studies, to empirical libraries for
population synthesis, to study of the local nebular environment and
feedback of massive stars in sub-solar metallicity environments.
Description:
Target list, journal of the observations and radial velocity
measurements of Large and Small Magellanic observations of the XShootU
ESO Large Program.
The DR1 data and an accompanying release documentation are made
available on Zenodo https://doi.org/10.5281/zenodo.11122188
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 92 232 List of XShootU target
table2.dat 90 324 Journal of the observations
tablea1.dat 131 232 Cross-identification
tablec1.dat 123 275 RV measurements
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See also:
J/A+A/675/A154 : X-Shooting ULLYSES. Project Description (Vink+, 2023)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 22 A22 --- Object Object identifier
25- 26 I2 h RAh Right ascension (J2000.0)
29- 30 I2 min RAm Right ascension (J2000.0)
33- 37 F5.2 s RAs Right ascension (J2000.0)
40 A1 --- DE- Declination sign (J2000.0)
41- 42 I2 deg DEd Declination (J2000.0)
45- 46 I2 arcmin DEm Declination (J2000.0)
49- 52 F4.1 arcsec DEs Declination (J2000.0)
55- 56 I2 --- nUVB Number of epochs in the UVB arm
59- 63 I5 s TexpUVB Cummulated integration time of UVB exposures
66- 68 I3 --- snrUVB Signal-to-Noise Ratio in coadded UVB spectra (1)
71- 72 I2 --- nVIS Number of epochs in the VIS arm
75- 79 I5 s TexpVIS Cummulated integration time of VIS exposures
82- 84 I3 --- snrVIS Signal-to-Noise Ratio in coadded VIS spectra (2)
87- 92 F6.2 d deltMJD Time difference between the start of the first
and last observing epochs.
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Note (1): Measured per rebined pixel on 0.02nm on the coadded and rebin UVB
spectra between 475 and 480nm.
Note (2): Measured per rebined pixel on 0.02nm on the coadded and rebin VIS
spectra between 675 and 685nm. See paper for exceptions.
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 22 A22 --- Object Object identifier
25- 33 F9.3 d MJD-UVB Modified Julian Date (JD-2400000.5) at
the start of UVB exposures
36- 39 I4 s Tex-UVB UVB exposure integration time
42- 44 I3 --- SNR-UVB Signal-to-Noise Ratio in rebin UVB spectra (1)
47- 55 F9.3 d MJD-VIS Modified Julian Date (JD-2400000.5) at
the start of VIS exposures
58- 61 I4 s Tex-VIS VIS exposure integration time
64- 66 I3 --- SNR-VIS Signal-to-Noise Ratio in rebin VIS spectra (2)
69- 84 A16 --- FluxStd Flux standard star used in the data reduction
87- 90 F4.1 d DeltaT Time difference between the start of the
science and flux observations
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Note (1): Measured per rebined pixel on 0.02nm on the rebined UVB spectrum
between 475 and 480nm.
Note (2): Measured per rebined pixel on 0.02nm on the rebined VIS spectrum
between 675 and 685nm. See paper for exceptions.
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Byte-by-byte Description of file: tablea1.dat
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Bytes Format Units Label Explanations
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1- 23 A23 --- XShootU XShootU target identifier (from Paper I)
26- 53 A28 --- OB Observing Block (OB) name, as stored in the
OBJECT keywords of the RAW data file
56- 83 A28 --- MAST MAST identifier, used for filenames and
OBJECT keywords of the HLSPs
86-108 A23 --- Simbad Simbad identifier
110-131 A22 --- Object Object identifier
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Byte-by-byte Description of file: tablec1.dat
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Bytes Format Units Label Explanations
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1- 28 A28 --- MAST MAST identifier of the star (1)
30- 38 F9.3 --- MJD Modified Julian Date of the start of
the observation (JD-2400000.5)
41- 45 F5.1 km/s RV Radial velocity
48- 50 F3.1 km/s e_RV Uncertainty on radial velocity (2)
53- 74 A22 --- Template Code of the template PoWR model used
77- 79 I3 km/s vsini Projected rotational velocity used in
cross-correlation
82 I1 --- Qual Quality of the fit (3)
85-100 A16 --- Com Comments about possible binarity (4)
102-123 A22 --- Object Object identifier
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Note (1): A given star can have multiple entries if there are multiple
observations more than 15 minutes apart.
Note (2): An underestimate in most cases.
Note (3): Low values indicate a bad quality and high values a good quality.
Note (4): EB = eclipsing binary, XB = X-ray binary.
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Acknowledgements:
Hugues Sana, hugues.sana(at)kuleuven.be
Frank Tramper, frank.tramper(at)kuleuven.be
Ronny Blomme, blomme(at)oma.be
References:
Vink et al., Paper I 2023A&A...675A.154V 2023A&A...675A.154V
(End) Hugues Sana [KUL, Belgium], Patricia Vannier [CDS] 07-May-2024