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Next: EMIR - a veritable Up: IRAM Newsletter 73 (September 2009) Previous: New IRAM Website


News from the 30m

EMIR Commissioning

The new Eight Mixer Receiver EMIR was installed and commissioned in March and April 2009. Routine observations started end of April.

The large bandwidths provided by EMIR, required a profound upgrade of the IF distribution at the 30m telescope. Inside the receiver cabin, an IF switch box was installed to select 4 outputs of 4GHz to be sent via new IF cables to the backend room. Three new processors, the 4MHz processor, the 4x4 WILMA processor, and the Narrow Backend Processor, were built to distribute the signals finally to the known set of backends.

Major parts of the telescope software had to be rewritten for EMIR. This concerns part of the "New Control System" and, of course, the PaKo user interface. In addition, the entire software producing the data had to be thoroughly revised: the read-out of the spectrometers into data streams, the transformation into IMBfits raw data, and the final transformation into calibrated data on the antenna temperature scale.

The observed alignment between the beams of the two polarisations and between the bands is very good. We derived telescope efficiencies from observations of Mars and from skydips, which show that the coupling of the EMIR beams to the telescope is as expected. All EMIR frequency setups of Bands 1 to 3, which had been requested for the running summer semester, were tested. Spectral line observations were conducted using the WILMA, 4MHz, and VESPA backends, using all standard observing modes. 3mm VLBI was tested together with the PdB and works well. A more detailed report is available on the EMIR web pages.

Routine observations with EMIR started on April, 28, without encountering major obstacles since then. During the first half of the semester (till mid-August), friends of EMIR have been designated to each observing project, to help with the setups. This extra effort is not continued, as well-tested template scripts exist by now. The Astronomer of Duty is the point of contact in case of questions. A number of projects, in particular extragalactic projects, profited greatly from the much enhanced bandwidths and noise temperatures of EMIR. Below, we present some first astronomical highlights.

What are the next steps? An external cold load and polarizer were installed for polarimetry, which we will try to make available to the general users in the course of this summer. First tests of band 4 showed that the Local Oscillator (LO) lacks output power and needs to be replaced. The measured aperture efficiency at 330 GHz is 30%, confirming the good surface accuracy of the 30m dish, allowing to enter the submillimeter domain. After installation of a new LO, full commissioning of band 4 is planned for October/November, during the HERA and MAMBO2 pool weeks.

Carsten KRAMER

First results with EMIR


Rebeca Aladro and here team used EMIR to carry out full spectral line surveys in the 3mm window of the ISM in several galactic nuclei. The aim of this study is to determine the evolution of the chemical complexity with starburst age in a sample of galaxies with different type of nuclear activity. One of the surveyed sources is the well known starburst galaxy M82. This galaxy was also previously observed by the same team using the old 2mm CD SIS receivers. Fig.1 shows the result of the frequency survey, covering both atmospheric windows, at 3mm and 2mm. While the 3mm survey was conducted in just 4 days with EMIR, the 2mm survey was conducted during 2years. The noise rms of both surveys is approximately the same, 2mK at 2MHz resolution. The on$+$off observing time for the 3mm survey was just only 11hours, about a factor of 9 faster than the 2mm survey, reflecting the huge gain in bandwidth which allows a significant quantitative and qualitative step forward in studies of the chemical complexity in Galaxies. Several transitions from more than 25 molecular species already detected in extragalactic objects provide unique information on the properties of the molecular gas. Thanks to EMIR, the tools to use molecular classification are now in our hands, to fully understand the evolutionary stage of the nuclear starburst. This work is part of the PhD thesis R.Aladro conducts at IRAM/Granada

Figure 1: Frequency survey of the nucleus of M82 by Aladro et al.. The 3mm spectrum shows the result of a quick reduction of EMIR data. The 2mm spectrum was taken with the old CD receivers.

Rebeca ALADRO and Carsten KRAMER

Figure 2: Two large-scale views of the B211-213 star-forming filament in the Taurus Molecular Cloud.

MAMBO2 pool observations in the period February to April 2009

Before the start of the MAMBO2 observing pool weeks, Albrecht Sievers carried out tests to check the present status of the MAMBO2 bolometer. In particular, the rotated wobbler observing mode was checked to be working perfectly, and was extensively used during this pool.

The pooled observations, in general, enjoyed good to excellent weather conditions reaching below 1mm of water vapor. However, almost two weeks were lost due to bad weather (wind and snow). During this pool session, the old ABCD heterodyne receivers were dismounted and EMIR was installed and commissioned. A total of 12 observing projects were finished, including several Targets-of-Opportunity (ToO) projects. These ToO projects included high-redshift objects, gamma-ray bursts, jets of an weakly accreting stellar black hole, and the comet Lulin. All were detected but the high-z objects.

The main technical problems during this period were spikes and the stability of the backend. The rate of spikes increased strongly relative to the November 2008 pool. The time distribution of spikes is currently investigated together with Robert Zylka. The ABBA2 backend showed the known problem of crashes about 2-4 times per day. This is under investigation together with Giorgio Siringo at the MPIfR. New, upgraded software has been installed after the pool, and is currently tested.

Among the science highlights of this pool session are: the detection of four new circumstellar disks around brown dwarf stars, and the detection of a proto-brown dwarf in rhoOph. Figure2 shows a map of the B211-213 filament in the Taurus region, which was obtained by Hacar et al..

The left part of Figure 2 shows C$^{18}$O and N$_{2}$H$^{+}$ emission as observed with the FCRAO telescope, while the right image presents a combination of a MAMBO2 map obtained during the March 2009 pool (right-top, above the dashed line) and a previously taken MAMBO2 map (Hacar et al. 2009, in prep.). As the images show, each spectral line tracer only provides a biased and incomplete view, due to freeze-out of C$^{18}$O from the gas phase, and chemical effects.

The 1.2mm continuum image illustrates how the dust emission is the only unbiased tracer of the star-forming region. It shows simultaneously both the extended gas and the dense cores, and provides the only means for determining the true density structure of the filament.

Carsten KRAMER

next up previous
Next: EMIR - a veritable Up: IRAM Newsletter 73 (September 2009) Previous: New IRAM Website