Long-slit Intermediate Resolution InfraredSpectrograph for the WHT
Proto-planetary nebulae (PPNe) are nebulae in which the central star is highly obscured by dust, there being no visible counterpart in the majority of cases. For this reason, they can be observed only in the infrared. By means of K-band spectroscopy it is possible to investigate the distribution of ionized and molecular gas. This permits an understanding of this rapid transition phase that later gives rise to the formation of a planetary nebula.
The IR is the most favorable spectral domain for detecting the contribution to the integrated light of a multiple system (binary or planetary) from the least massive components. IR intermediate-dispersion spectroscopy can permit the detection of molecular bands (H2O and CO) from very cool objects superimposed on the continuum of the primary. A particularly interesting case is that of the recently discovered planets at less than 0.5 AU from their stars. The temperature of these planets must be high enough for them to have their emission peak in the near IR, i.e. in the spectral range of LIRIS.
Furthermore, red colours do not constitute a unique identification of brown dwarfs, whereas infrared spectroscopy in the wavelength range of LIRIS would allow the methane bands characteristic of an atmosphere sufficiently cool for a brown dwarf to be stand out.
The existence of a population of galaxies at around
z=1 with active star formation, probably of low metallicity and with blue
colours has recently been demonstrated by the spectroscopic surveys carried
out on the Keck telescope. The possibility that these objects constitute
a population of dwarf galaxies in the process of developing the first bursts
of star formation is extremely interesting, since they would enable us
to find objects of metallicities < 1/100 solar, which might reflect
the optimum representation of the pregalactic abundances necessary for
deriving a precise value of the primordial abundances. In this way we could
intercompare the spectroscopy of our local surroundings with that at other
redshifts and thus unravel some of the so far unresolved problems of their
The presence of dust in the center of spiral galaxies means that the ideal spectral range for their studies is the infrared. In particular, we shall be able to determine kinematic peculiarities and their correlation with the stellar populations at the centers of galaxies without the uncertainty that arises in the visible range. This will enable us to understand the nature and mechanisms of the formation of bulges, discs, bars and dynamical subsystems such as counterrotating discs and bulges.
Galaxies with high luminosity in the far infrared, denominated "ultraluminous infrared galaxies" (ULIRGs) exhibit violent star formation owing to interaction processes. Such galaxies have huge quantities of dust thereby rendering their study in the visible quite impracticable. LIRIS will enable us to study such galaxies in order to investigate whether they really constitute the progenitors of elliptical galaxies.
With LIRIS it is intended to study the physical conditions of the gas, and the kinematics and formation of stars in galaxies with massive star formation and high extinction in their centers. With this project two objectives may be addressed: first, the determination of the origin and age of the bursts of star formation in isolated dwarf irregular galaxies, and secondly the study of nuclear starbursts in galaxies that show bars and/or AGNs. In this context, the study of the underlying stellar populations may be undertaken using the CO absorption band at 2.3 m m, as well as the study of the physics of the gas with lines such as FeII at 1.65 m m, Brg and HeI at 2.06 m m and H2 at 2.12 m m. With the same spectral lines we can determine the gas stellar kinematics, which will give us the dynamics of the nuclear zones since such measurements in the visible wavelength range are severely affected by dust. Such observations will help us to understand the starburst phenomenon.
The Hubble Space Telescope has shown that the morphological classification of galaxy clusters at redshift z=0.5 can be undertaken. The colour-magnitude diagram of one of these clusters reveals elliptical, S0 and a large population of late spiral and irregular galaxies. LIRIS will allow the study of the stellar dynamics and populations of elliptical and S0 galaxies in such clusters. Hence, spectroscopic measurements in the IR could provide the velocities of dispersion and the spectral indices of the stellar component of such galaxies using such species as the CaII triplet. With such measurements, we could obtain the fundamental plane of the high-redshift elliptical and S0 galaxies and compare it with the nearby galaxies in order to understand their formation and evolution.
The large-scale infrared surveys such as 2MASS and ISO will provide an enormous quantity of infrared sources, from stellar objects to galaxies, which will have to be classified. In this context, LIRIS provides us with a very useful tool, since with the expected limiting magnitude we could obtain the spectroscopic counterparts of the said sources. For example, given the limiting magnitude of the 2MASS survey (K=15) we could obtain an S/N=20 spectrum on the WHT with some 10 minutes? integration time.
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