J/A+A/547/A85 Spectra of 7 Hα emission line stars in MBM 18 (Brand+ 2012)
Molecular gas and stars in the translucent cloud MBM 18 (LDN 1569).
Brand J., Wouterloot J.G.A., Magnani L.
<Astron. Astrophys. 547, A85 (2012)>
=2012A&A...547A..85B 2012A&A...547A..85B
ADC_Keywords: Molecular clouds ; Stars, emission ; Spectroscopy
Keywords: stars: formation - stars: emission line - ISM: clouds -
ISM: individual objects: MBM 18 (LDN 1569)
Abstract:
We investigate star formation in translucent, high-latitude clouds.
Our aim is to understand the star-formation history and rate in the
solar neighbourhood.
We used spectroscopic observations of newly found candidate Hα
emission-line stars to establish their pre-main-sequence nature. The
environment was studied through molecular line observations of the
cloud (MBM 18/LDN 1569) in which the stars are presumably embedded.
Description:
Data in tabular form (wavelength and flux) are presented of the
spectra of seven candidate Hα emission line stars in the
direction of translucent cloud MBM 18.
The data were obtained on 5 different nights in 2009 and 2010 with the
3.58-m Telescopio Nazionale Galileo (TNG; La Palma, Canary Islands,
Spain). The spectra are shown in the appendix of the paper, only
visible in the on line version.
The spectra were taken with the low-resolution spectrograph DOLORES on
the TNG, using long-slit spectroscopy.
We used grism VHR-R, which covers a wavelength range of 6240-7720
Angstrom with a dispersion of 0.80Å/pix. The scale of the CCD
detector is 0.252 arcsec/pixel. The observations were carried out with
a slit width of 1 or 1.5 arcsec, depending on the seeing, resulting in
a spectral resolution of 3.2Å and 4.8Å, respectively.
To avoid problems with cosmic rays, 2 to 4 separate spectra per star
were obtained. Two of the stars (Ha4 and Ha6) were observed
simultaneously with another target (Ha1 and Ha5, respectively) by
positioning the slit at an appropriate angle. The integration time was
based on the brighter star in the slit, thus the signal-to-noise ratio
for the other target is smaller than for the primary one.
To allow absolute flux calibration the standard star Feige24 or
Feige34 (for Ha5-Ha6) was observed immediately before or after the
target observations, using the same instrumental setup as for the
target observations. Flat-fielding was performed using 10 (5 for
Ha5-Ha6) frames, which were uniformly illuminated by a halogen lamp.
Wavelength calibration was performed using an arc-spectrum of an Ar,
Ne+Hg, and Kr lamp, or a Ne+Hg (for Ha7) comparison lamp.
A bias frame, to be subtracted from the other frames before analysis,
was constructed from ten individual bias frames. Flat-, arc-, and
bias-frames were obtained on the same day as the science observations
and with the same instrumental setup.
Data were reduced with the IRAF package. From all science frames a
bias was subtracted, after which they were divided by the normalised
flat field. From each of the science frames the trace(s) of the
star(s) were extracted and these were wavelength-calibrated using one
of the frames with the arc-spectrum. Each target was
wavelength-calibrated with the arc-spectrum extracted at the same
location on the detector, to compensate for small deviations that
might occur in the alignment of the reference emission lines across
the detector. The spectra were then corrected for extinction, and
flux-calibrated using the standard star observations. The individual
one-dimensional wavelength- and flux-calibrated spectra of each target
were then averaged into a final spectrum. To further correct the
wavelength calibration, we used the sky lines that were subtracted
from the stellar spectra. For each spectrum, Gaussian fits were made
to tens of sky lines, and their wavelengths were compared to those
listed in Osterbrock et al. (1996PASP..108..277O 1996PASP..108..277O, Cat. III/211. Three
stars were found to need a small correction: Ha2 (-1.5Å) and Ha5 and
6 (both -2.2Å); these corrections have been applied in the tables.
For the other four stars the difference was negligible, although for
the sky lines in Ha1 and Ha4 (which were observed in the same slit)
the deviation between measured and literature wavelengths varied
slightly, but systematically, with wavelengths between 6250Å and
7600Å, while at longer wavelengths the deviations became rapidly
larger (up to several Angstroms).
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 108 10 Coordinates and magnitudes of the candidate
Hα emission-line stars, and log of TNG
observations
fig_a1a.dat 22 2036 Wavelength and flux for star Ha1
fig_a1b.dat 22 2036 Wavelength and flux for star Ha2 (skyline
correction to wavelength scale has been applied)
fig_a1c.dat 22 2036 Wavelength and flux for star Ha5 (skyline
correction to wavelength scale has been applied)
fig_a1d.dat 22 2036 Wavelength and flux for star Ha6 (skyline
correction to wavelength scale has been applied)
fig_a1e.dat 22 2036 Wavelength and flux for star Ha7
fig_a1f.dat 22 2036 Wavelength and flux for star Ha8
fig_a2.dat 22 2036 Wavelength and flux for star Ha4
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Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 4 A4 --- Star Star name (HaNN)
6- 7 I2 h RAh Right ascension (J2000)
9- 10 I2 min RAm Right ascension (J2000)
12- 16 F5.2 s RAs Right ascension (J2000)
18 A1 --- DE- Declination sign (J2000)
19- 20 I2 deg DEd Declination (J2000)
22- 23 I2 arcmin DEm Declination (J2000)
25- 28 F4.1 arcsec DEs Declination (J2000)
30- 34 F5.2 mag Fmag GSC photographic F magnitude (1)
36- 40 F5.2 mag Vmag GSC photographic V magnitude
42- 46 F5.2 mag Jmag 2MASS J magnitude
48- 52 F5.2 mag Hmag 2MASS H magnitude
54- 58 F5.2 mag Kmag 2MASS K magnitude
60- 69 A10 "DD/MM/YYYY" Obs.Date TNG observation date
71- 76 A6 s Int.Time Integration time(s)
78- 96 A19 --- Com Comment
98-108 A11 --- FileName Name of the file containing the spectrum
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Note (1): Fmag approximately corresponding to the Johnson R-mag.
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Byte-by-byte Description of file: fig_*.dat
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Bytes Format Units Label Explanations
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2- 9 F8.3 0.1nm lambda [6100/7900] Wavelength of observation
11- 22 E12.6 cW/m2/nm Flux Flux (in erg/cm2/s/Å)
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Acknowledgements:
Jan Brand, j.brand(at)ira.inaf.it
(End) Patricia Vannier [CDS] 05-Oct-2012