First Scientific Results obtained with LIRIS
Jose A. Acosta Pulido, A. Manchado Torres,
M. CharcosCharcos-Llorens♣, O. GonzalezGonzalez-Martin♠, M.J. Vidal Nuñez ♠
Instituto de Astrofísica de Canarias
♣ Now at Dpt of Astronomy at Univ of Florida
♠Now
at Instituto de Astrofisica de Andalucia
LIRIS is a near infrared (0.9-2.4 microns) imager and spectrograph built by the Instituto de Astrofísica de
Canarias (IAC). It was conceived as a common user instrument for the William Herschel Telescope at the
Observatorio del Roque de los Muchachos (ORM La Palma). Currently LIRIS includes imaging and spectroscopic
observing modes. Spectroscopy is done using long-slit and also a number (~8) of multi-object masks can be
inserted. Grisms are used as the dispersion elements. Two spectral configurations are available, one covers the
bands Z and J, and the other the bands H and K, with similar resolution of 650. The image capability allows easy
target acquisition.
It also contains a coronographic mask. Imaging and spectropolarimetry will future upgrades.
The optical system is based on a classical collimator/camera design. The plate scale (0.25 arsec/pixels) matches
the median seeing (0.6 arcsec in the K band) at the ORM. The detector is a Hawaii 1024x1024 HgCdTe array
operating at 70 K.
Predefined Observing sequences:
Multipoint dither
LIRIS attached to the Cassegrain platform
at the William Herschel Telescope.
Multipoint dither+sky for extended objects (<4’)
Mosaic for very extended objects (>4’)
Deep field mosaic
Nodding along slit for spectroscopy
Milestones
Feb 03: First commissioning run
Mar 03-Jan 04: Upgrading at IAC
Mar 04: Second commissioning run
Aug 04: Public use (CAT/PATT)
Oct 04: Polarimetry Commissioning
Feb 05: Upgrade to R~2500
The optical quality of the images is very
good. In this frame the PSF has a mean value
of 0”.6 with variations < 0”.15 across the
field. The geometrical distorsion from center
to corner is ~1”.5, and has to be taken into
account when combining images or for
astrometry purposes.
Offbeam for spectroscopy of extended objects
Pseudo 3-D spectroscopy for extended objects
Mcneil nebula: the birth of a star
The Comet C2001/Q4 Neat
J, and Ks band images of the comet
Q4 Near were obtained in June 2004
during its passage close to the Sun. In
this picture the pink region represent
the Ks emission whereas the blue
corresponds to the J band.
McNeil nebula was discovered at the beginning of 2004. The nebula
is illuminated by an eruptive low mass pre-main sequence star,
which suddenly increases its brightness by several magnituedes.
This phenomenon is very rare and therefore attracts many observers.
The object is embedded in the Lynds 1630 dark cloud in Orion. The
mechanism producing the outburst is likely due to instabilities in the
inner part of the accretion disk.
Near IR spectra were also obtained
with LIRIS, the emission of the
comet was detected in the whole slit
length (4’). Several prominent
features are detected in emission,
likely due to CH4.
Spectra were taken with LIRIS
in March 2004. The main
features are H emission lines,
turning to absorption at high
levels. Dense stellar winds
produces this type of spectra.
Composite image in the
visible colours V, R and I
(Reipurth & Aspin, 2004).
The illuminating star
V1467 sit at the apex of
the nebula.
Composite image in J, H and
Ks obtained by LIRIS. The
near IR images looks different
than the optical ones, the
nebulosity shows a U shape.
There is also an extension to
the S of the illuminating star.
H-K color map showing a
very red structure at the
S of the nebula. The
variation of near IR
colours across the nebula
is compatible with a V
extinction of 15 mag.
Brown dwarfs and substellar objects
A L0 dwarf companion to the M star G239-25
Extragalactic studies
A spectrum of the most known distant QSO (z=6.4)
The star G239-25 is nearby
M1.5 dwarf. The companion
was detected in adaptative
optics images at the CFHT
(Forveille et al, 2004), at a
distance of 3” and ∆m~4. The
projected distance is 31 AU.
The spectrum of the companion
was extracted by fitting Moffat
profiles to both components.
The measurements of emission lines of very
high z quasars permit to investigate the
metallicity of galactic nuclei at large
cosmological distances. In this way the star
formation history can be traced to very early
epochs of the Universe (Hamman & Ferland,
1999).
Based on LIRIS spectrum G239-25B is
classified spectroscopically as an L0
dwarf (Forveille et al., 2004).
Searching for substellar mass objects
A spectrum of the most distant quasar known
at that time, covering the Z and J bands was
obtained during the first commissioning
period. The spectrum shown here was
obtained with total integration time of 70
min. The most intense line is the CIV detected
with a S/N ratio of 10.
from wide field images
These objects are in general very faint and the near IR colours are needed in order
to confirm or discard its substellar nature. An spectroscopic classification becomes
very difficult due to its faintness. Several deep images in Ks band were obtained with
LIRIS of selected fields where candidates for substellar objects were present.
The object S Ori 3-1-756 was selected due to its color I-J (I>24.3, J=21.4). LIRIS
photometry (H=19.98 and Ks=18.65) results in a very intriguing red object, it could be a
background galaxy or a low mass object with an infrared excess. Its true nature can
only be determined after a spectroscopic study.
Two other fields were observed in June 2004 dedicating 1 hour of exposure time
reaching a limiting magnitude Ks~19.3. One candidates was found to have Ks=17.04 and
is likely an L dwarf. The other candidate resulted to be a moving object, likely an
asteroid.
Measuring faint and close companions of very bright stars.
An application of coronographic capabilities.
In June 2004 the bright variable star V383 Lac (Ks=6.5)
was observed using a coronographic mask (1.5 arcsec).
There was an object selected as candidate to be a
substelar companion of V383 Lac at a distance of 10”, the
magnitude difference is 8 mag. LIRIS images (J and Ks)
allow to measure the proper motion of the object (<
7mas/year) and discard it as a companion since the proper
motion of V383 Lac is 94 mas/year. A very faint object
(Ks=17.5) could be clearly observed at a distance of ~10“.
The gravitational lense SBS0909+532
This system consists of a double quasar formed by a bright component plus a fainter component one
at z=1.38, with a possible lensing galaxy at z=0.83 (Oscoz et al, 1997).
The separation of the two components
is only 1”.14, requiring good seeing
conditions for its observation.
The ZJ band spectrum obtained by LIRIS
allows to study the two components
separately. It can be noticed the different
amplification factor for continuum and
emission lines, giving account for the different
size of the emission regions (the central
engine, the Broad and the Narrow Line
regions)
Multiobject spectroscopy
Multi-object spectroscopy has been tested using
masks over bright calibration stars. This mode
has still to be validated using faint targets.
Up to 8 multiobject masks can be mounted in
LIRIS. Mask exchanges will happen every
semester. .
References:
Acosta-Pulido, et al, 2003, ING Newsletter, 7, 15
Acknowledgements:
Forveille et al., 2004, A&A accepted.
LIRIS would not be reality without the enormous effort of many people
from Instrumentation and Research Areas at the IAC. We would also like
to thank J.A. Caballero and M.T. Costado for providing information
about the search of brown dwarfs performed with LIRIS.
Hamman & Ferland, 1999, ARA&A 37, 487
Kun et al, 2004, A&A submited
Oscoz et al., 1997, Ap.J. 491, L7
Several science programs are foreseen
for this mode: measuring Ha at star
forming galaxies at z~1, spectral
classification in obscured star clusters
and star formation regions.
The mask design procedure has been tested
and the errors were found to be below 0”.25
The crutial points are astromety better than
0”.1 and good reference stars.