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Paper text:
deuterium is an element of primordial origin .
measuring its abundance in different astrophysical sites brings valuable constraints on the big - bang nucleosynthesis and the galactic evolution (  lemoine et al .
@xcite ) .    the detection and identification of the deuterium balmer lines  and  in emission in the orion nebula was first reported by hbrard et al .
( @xcite , hereafter paper  i ) .
the narrowness of these lines , their strength with respect to the hydrogen lines and finally their relative fluxes were incompatible with recombination excitation , but could be understood in terms of fluorescence excitation by stellar uv continuum in the photon dominated region ( pdr ) , located behind the ionized region .    here , observations of the whole balmer series with the new spectrograph uves , installed at the nasmyth focus of vlt - ut2 , are presented for orion and other  regions .
observations are described in sect .
[ observations ] .
results for each  region are presented in sect .
[ results ] .
new evidence in support to the identification of deuterium is discussed in sect .  [ discussion ] .
a more complete analysis will follow in forthcoming papers .
observations were secured during the night 2000 july 25th-26th , using the uv - visual echelle spectrograph ( uves ) located at the nasmyth focus of kueyen , the second vlt unit telescope ( dodorico & kaper  @xcite ) .
spectra from both the red and blue arms were registered simultaneously on two detectors , using the standard setting dic1  ( 390 + 564 ) .
the approximate spectral ranges were 3290  -  4530  ( blue arm ) , and 4610  -  5620     and 5660  -  6660  ( red arm ) , encompassing the whole balmer series .
the slits were 8  and 11  long for the blue and red arms respectively .
the slit width was 1  on the sky . according to the staff of the vlt , the spectral resolution was @xmath0 ( full width at half maximum , fwhm ) , equivalent to @xmath1 .
the present conclusions do not depend on the exact value of @xmath2 , which will be determined after reducing the calibration exposures .
a total exposure time of one hour was devoted to each  region ( except for orion , sect .
[ m42 ] ) , the observations being divided in short sub - exposures to prevent detector saturation at the  balmer lines .
data reduction ( bias subtraction , flat - fielding , wavelength calibration ) was performed with the uves pipeline , using the available calibration database .
1d spectra were box - extracted from the central third of the slits .
the standard sky - subtraction algorithm , inappropriate for extended objects , was omitted .
this extraction was judged robust enough for this preliminary study .
subsequent data reduction will be performed over the whole slit length , using the calibration exposures obtained during the observing run .
cosmics and bad pixels were cleaned where necessary .
sub - exposures were averaged ( no shift was observed from one sub - exposure to the next ) and the lines were shifted to the same radial velocity . for a given object ,
the peak fluxes of the different lines were assigned the same value in order to display the relative variations of the weak lines ( figures of sect .  [ results ] ) .
shifts and normalizations were all based on gaussian fits to the emission lines .
line detections reported here in the blue wings of the  lines are at least at the 5-@xmath3 confidence level . most of them are confirmed by the detection of lines at the same velocity for several principal quantum numbers @xmath4 .
the area observed in orion was the same as the one observed previously ( paper  i ) .
the slit , oriented north - south , was located 2.5  south of @xmath5  ori  c ( ) at coordinates @xmath605:35:16.7 , @xmath705:25:29 ( j2000 ) .
the exposure time was 30  min in the red arm and 50  min in the blue arm .
plots of the  balmer line wings are shown in fig .
[ m42_fig ] .
deuterium lines are detected from  to .
they are redshifted @xmath8  with respect to  ( the isotopic shift between  and  at rest is @xmath9 ) , in good agreement with the previous measurements ( paper  i ) .
lines seem to be detected up to d16 , but elaborate treatment is required due to low signal - to - noise ratio .
fwhm are from gaussian fits , after quadratic subtraction of the instrumental point - spread function .
the fwhm of the  lines is @xmath10 , much less than that of the  recombination lines ( @xmath11 ) .
widths similar to these were found for the lines detected in m  8 , m  16 , m  20 and dem  s  103 ( see below ) . from fig .
[ m42_fig ] , it is apparent that  increases relative to  for increasing @xmath4 , at least up to .
approximate relative fluxes are given in table  [ table_m42 ] . despite lower signal - to - noise ratio
, a similar trend exists in the data for m  8 and m  16 .
.preliminary line flux ratios in m  42 [ cols="^,^,^,^,^,^",options="header " , ]     @xmath12 colons indicate low - accuracy values ( from  and  only ) . + @xmath13
average shift of  with respect to  ( ) .
+ @xmath14 average fwhm of the  lines ( ) .
+    the new observations bring confirmatory evidence in favour of the identification of the deuterium balmer lines .
they complement and add to the results presented in paper  i. the lines are seen with similar characteristics in the five  regions , using different telescopes ( cfht and vlt ) and different spectrographs ( gecko and uves ) .
instrumental artifacts ( such as grating ghosts or in - order scattered light ) can be definitely ruled out .
since the lines are seen for many members of the balmer series , they can only be  or blue - shifted  emission .
emission may arise from h@xmath15 gas ( recombination ) or h@xmath16 gas ( fluorescence ) .
high - velocity ionized structures will produce  recombination lines with properties like those already listed in the case of m  17 ( width , flux , counterparts ) , not observed in the other  regions described in sect .
[ results ] .
a high - velocity neutral structure can not be formally excluded for any one isolated object , but the probability that such a structure could exist and yet be detectable only in  is low .
no evidence for the existence of such a structure could be found in the case of orion ( paper  i ) .
considering the present data , it would be extraordinary if such a neutral component could be present in such a systematic manner in five different  regions , always at about the same velocity .    understandably , the  lines are narrow since they arise from a cold material with small thermal velocity .
nonetheless , considering the prevalence of large velocity fields in  regions , it was not a priori obvious that these lines would appear so systematically narrow ( table  [ lines ] ) .
the explanation partly lies in the fact that the entrance aperture of uves is relatively small and that observable  regions tend to be incomplete on one side , with the associated molecular cloud and pdr located behind the expanding h@xmath15 region .
this is consistent with the tendency shown by the  lines to be redshifted with respect to the  lines ( table  [ lines ] ) .
thus , in practice , a small line width ( at the expected wavelength ! ) turns out to be an important criterion to identify . on the other hand
,  regions may exist with pdr s encompassing a large velocity range .
a fundamental criterion for  identification remains the lack of counterparts in lines from ionized species .
large variations of the line intensity ratio /  with @xmath4 constitute another useful criterion ( table  [ table_m42 ] ) , since fluorescence will generally not result in the same decrement as the one corresponding to recombination .    as a result of the present high spectral resolution and high signal - to - noise observations ,
the identification of deuterium balmer lines is now very safe .
detection of deuterium balmer emission in five  regions is reported .
these are first detections in four targets , including an extragalactic one .
detection was made feasible thanks to the large collecting area of the 8.2 m vlt mirror and the high efficiency of uves .
fluorescence is confirmed as the probable excitation mechanism of , recombination being excluded .
spectroscopic criteria leading to virtually certain identification of  in any given  region are now clearly established .
possible ways to determine d / h from  balmer lines were discussed in paper  i. one method requires a knowledge of the @xmath4 for which the line ratio /  starts decreasing .
the detection of  up to d9 , and possibly d16 , in orion suggests this as a promising way of investigation .
comparison of  to  fluorescence lines , present in the uves spectra and also produced in the pdr , may be another way to explore .
the search for deuterium balmer lines with vlt - uves is reported in  regions of the galaxy and the magellanic clouds . 
 the  lines appear as faint , narrow emission features in the blue wings of the  balmer lines and can be distinguished from high - velocity  emission . 
 the previous identification to deuterium is re - inforced beyond doubt .    
 the detection of  and  in orion ( hbrard et al .  
 @xcite ) is confirmed and deuterium lines are now detected up to at least . 
 the uves observations provide the first detection of balmer  lines in four new  regions ( m  8 , m  16 , m  20 , and dem  s  103 in  smc ) , demonstrating that these lines are of common occurence .