UVES observations in BRASS
P.A.M. van Hoof
Royal Observatory of Belgium
and the BRASS consortium
UVES Observations (1) Eight stars in BRASS have been observed with UVES.
● 51 Peg: G2IV, only dic1 available, flatfield problems?
● 2014-07-21 (1 spectrum)
● 2014-07-31 (48 spectra), S/N ~ 275
● 2014-09-28 (198 spectra), S/N ~ 265
● 2014-10-28 (44 spectra), S/N ~ 255
● Arcturus: K1.5IIIFe-0.5, 2003-02-17, S/N ~ 1000?
● 15 blue + 14 red spectra
● HD209100 (eps Ind): K4V, 2004-09-24, only dic1 available, S/N ~ 1000?
● 95 spectra with iodine cell
● 79 regular spectra
● HD221507 (beta Scl): B9.5III, 2008-05-27, only dic1 available, S/N ~ 450.
● 9 blue + red spectra UVES Observations (2)
● HD73634 (e Vel): A6II, 2003-01-03, S/N ~ 480.
● dic1: 5 blue + 7 red spectra
● dic2: 3 spectra
● HD74272 (n Vel): A5II, 2001-11-19, S/N ~ 500.
● dic1: 3 blue+red spectra
● dic2: 2 blue+red spectra
● HD90264 (L Car): B8V, 2002-02-26, S/N ~ 380.
● 2 blue+red spectra
● Procyon: F5IV-V, 2013-10-08, red spectra dic2 only, S/N ~ 330.
● 8 blue+red spectra
FEROS Observations For one star we have a FEROS spectrum consisting of 4 exposures.
● HD90264 (L Car): B8V, 2015-06-28, S/N ~ 260.
In the following slides we will identify several problems in the spectra, and we will also do a detailed study of the wavelength calibration of the spectra.
UVES data reduction
Christophe did an effort to reduce the wiggles. These have been greatly reduced, but have not disappeared completely.
As an example, part of the spectrum of HD 73634 is shown above.
UVES data reduction
Sometimes there are jumps in the spectrum, presumably where orders are joined. They are quite rare and typically at the 1-2% level.
As an example, part of the spectrum of HD 221507 is shown above.
51 Peg
For 51 Peg, averaging the spectra does not improve the S/N very much. Shown are all 44 spectra from 2014-10-28 in blue, and the average in red. There appear to be pixel-to-pixel variations that are reproduced in all spectra. This may indicate a problem with the flatfielding.
HD 90264
For HD 90264 we can compare the UVES and the FEROS spectrum from 2002 and 2015, resp. The Hα line appears to have a varying emission component in the center. This is confirmed in higher Balmer lines (up to H I 9 → 2). However, looks are deceiving! What we see here is a spectroscopic binary.
HD 90264
Shown here are the He I λ 4471 and Mg II λ 4481 lines. Especially in the latter we can clearly see the two components. The red component aligns exactly, while the blue component is shifted by 20 km/s.
HD 90264
The red component may show the presence of the Hg II λ 3984 line and may therefore have a HgMn abundance anomaly. See also Hubrig & Mathis (1996) A&AS 120, 457.
Individual remarks ● 51 Peg: double or multiple star; has a jupiter-mass substellar companion; possibly a variable star due to magnetic activity; member of the Pleiades moving group; a HERMES spectrum will also be offered in the BDI.
● Arcturus: RGB star; marked as a suspected variable star (Kukarkin+ 1981); a HERMES spectrum will also be offered in the BDI; is used as a standard reference atlas for line identification (Hinkle+ 2000).
● HD 209100: high proper motion star; spectral type is listed as K4V in annotation; this star has two brown dwarf companions of type T1V and T6V (Scholz+ 2003; McCaughrean+ 2004).
● HD 221507: has a HgMnSi abundance anomaly.
● HD 73634: none.
● HD 74272: none.
● HD 90264: SP2 type spectroscopic binary. Hubrig & Mathys (1996) list this star as He weak. It shows the HgMn abundance anomaly.
● Procyon: spectroscopic binary, companion is a DQZ white dwarf; rotational variability as a result of magnetic activity (Baliunas+ 1996); a HERMES spectrum will also be offered in the BDI. Wavelength calibration HD 90264
For HD 90264 we can also compare the wavelength calibration of the UVES and the FEROS spectrum by overplotting them. Shown are telluric lines from the O B band. There is a clear shift! This is investigated further in the following 2 slides.
HD 90264, UVES vs HITRAN
Shown is a comparison of the telluric lines from the O B band with HITRAN. 2 Average shift = -0.47 km/s, sigma = 0.12 km/s.
HD 90264, UVES vs HITRAN
Shown is a comparison of the telluric lines from the O A band with HITRAN. 2 Average shift = -0.57 km/s, sigma = 0.14 km/s.
HD 90264, UVES vs HITRAN
Shown is a comparison of various telluric lines from H O with HITRAN. 2 Average shift = -0.63 km/s, sigma = 0.18 km/s.
HD 90264, FEROS vs HITRAN
Shown is a comparison of the telluric lines from the O B band with HITRAN. 2 Average shift = -11.0 km/s, sigma = 0.17 km/s.
HD 90264, FEROS vs HITRAN
Shown is a comparison of the telluric lines from the O A band with HITRAN. 2 Average shift = -11.1 km/s, sigma = 0.13 km/s.
HD 90264, FEROS vs HITRAN
Shown is a comparison of various telluric lines from H O with HITRAN. 2 Average shift = -11.0 km/s, sigma = 0.23 km/s.
51 Peg vs the Sun
Shown is a comparison of graded lines measured in the Sun and 51 Peg using UVES. Most lines agree excellently, with some outliers. Average shift = -0.2 km/s, sigma = 1.5 km/s, MAD = 0.060 km/s. Worst outlier is at -10 km/s.
Other spectra vs HITRAN
We carried out a comparison of the observed and laboratory wavelengths of telluric lines in all UVES spectra using either the O B band, or H O lines in the 2 2 range 6455 – 6535 A. The results are consistent with what we found before.
wavelength calibration
● In the UVES spectra, the wavelength calibration seems to be in excellent shape!
● Most tests show a random error less than 0.2 km/s and a systematic shift better than 0.6 km/s. Some trends are visible, but only on a very low level. This is known as a drift of the wavelength calibration and is a common (and unexplained) feature in many spectrographs.
● In the FEROS spectrum we also see excellent values for the random error which are less than 0.25 km/s. This is slightly worse than UVES, but that is expected since the instrument has slightly lower resolving power.
● The FEROS spectrum shows a systematic shift of -11.0 km/s. This is far too big to be a calibration error. The most plausible explanation is that this spectrum was corrected for the Earth’s motion as the shift to heliocentric velocity would be -11.21 km/s.