4MOST: the 4-metre multi-object spectroscopic telescope project in the assembly, integration and test phase

4MOST is a new high-multiplex, wide-field spectroscopic survey facility under construction for ESO's 4m-VISTA telescope at Paranal, Chile. Its key specifications are: a large field of view of 4.4 square degrees, a high multiplex fibre positioner based on the tilting spine principle that positions 2436 science fibres in the focal surface of which 1624 fibres go to two low-resolution optical spectrographs (R = λ/Δλ ~ 6500) and 812 fibres transfer light to the high-resolution optical spectrograph (R ~ 20,000). Currently, almost all subsystems are completed and full testing in Europe will be finished in spring 2023, after which 4MOST will be shipped to Chile. An overview is given of instrument construction and capabilities, the planned science of the consortium and the recently selected community programmes, and the unique operational scheme of 4MOST

4MOST : the 4-metre multi-object spectroscopic telescope project in the assembly, integration, and test phase

4MOST is a new high-multiplex, wide-field spectroscopic survey facility under construction for ESO's 4m-VISTA telescope at Paranal, Chile. Its key specifications are: a large field of view of 4.4 square degrees, a high multiplex fibre positioner based on the tilting spine principle that positions 2436 science fibres in the focal surface of which 1624 fibres go to two low-resolution optical spectrographs (R = λ/Δλ ~ 6500) and 812 fibres transfer light to the high-resolution optical spectrograph (R ~ 20,000). Currently, almost all subsystems are completed and full testing in Europe will be finished in spring 2023, after which 4MOST will be shipped to Chile. An overview is given of instrument construction and capabilities, the planned science of the consortium and the recently selected community programmes, and the unique operational scheme of 4MOST

Vahakiinnityksen vaikutus piikiekon muotoon kiillotusprosessissa

Tässä insinöörityössä on tutkittu, kuinka vahakiinnitys vaikuttaa piikiekkojen muotoon kiillotusprosessissa. Aluksi on tutustuttu piikiekon mekaanisiin ominaisuuksiin, jonka jälkeen on kuvailtu yksipuolisesti kiillotetun piikiekon valmistusprosessi. Vahan levityksen vaiheet on käsitelty yksityiskohtaisesti spinnauksen teoriaan osittain nojautuen. Piikiekkojen tasomaisuuden mittaamista varten on suunniteltu ja rakennettu Newton-interferometri. Optisella mittalaitteella voidaan piikiekon tasomaisuus mitata tarkasti käyttäen hyväksi valon interferenssiä. Newton-interferometrin toiminta- ja mittausperiaate on esitelty yksityiskohtaisesti. Tasomaisuuteen vaikuttavat mahdolliset parametrit on kartoitettu. Piikiekkojen tasomai-suuden kannalta tärkeiksi nähtyjä parametreja on tutkittu viiden eri kokeen avulla. Kokeista on tehty tarkat koesuunnitelmat käyttäen hyväksi MODDE-ohjelmistoa. Viidessä kokeessa on tutkittu usean eri vahakiinnitysparametrin vaikutusta piikiekon muotoon. Tutkittavina muuttujina on käytetty spinnerin pyörimisnopeutta, vahan määrää, piikiekon painamista voimalla kiillotusalustaa vasten, vakuumiprässiä, sekä lämpötiloja vahakiinnityksessä. Lisäksi on kokeiltu kahta eri vahaa, joilla on eri viskositeetit. On havaittu, että suurin vaikutus piikiekon tasomaisuuteen on spinnauksen pyöritysnopeudella. Tasomaisuuden on havaittu paranevan spinnauksen pyöritysnopeuden ollessa korkea. Myös tasomaisuuden keskihajonnan on todettu pienenevän huomattavasti korkeilla pyöritysnopeuksilla. Lämpötilagradienttien on havaittu heikentävän piikiekon tasomaisuutta vahakiinnityksessä.The effect of wax mounting on the flatness of the silicon wafer in a polishing process is studied in the experimental part of this thesis. In the theoretical part of the thesis the mechanical properties of silicon wafers are summarized and the manufacturing process of silicon wafers is presented. In addition, the theory of wax spin coating is described in detail. In order to measure the flatness of a silicon wafer, mounted on a polishing carrier, a Newton Interferometer was designed and built. Using this optical measuring device, the flatness of the silicon wafer could be measured based on the interference of light. The theory behind the interferometer is described in detail. It is also described how a flat surface can actually be measured from an interferogram. A number of parameters that could potentially have an effect on the silicon wafer flatness in the wax mounting are determined. Parameters that are thought to be critical, in terms of the wafer flatness, are tested in five separate experiments. Each experiment is designed and carried out based on DOE principles. The MODDE software is used to design the experiments. In these five experiments variables such as the spinner rotation speed, wax amount, bonding arm pressure, vacuum press, and the temperatures on the silicon wafer flatness are studied after mounting the wafers on a carrier. Also two mounting waxes with different viscosities are tested. The spinner rotation speed is found to be the most important parameter on the silicon wafer flatness. With a high rotation speed the flatness of the silicon wafer is found to be the most substantial. The standard deviation of the wafer flatness is also significantly smaller with high rotation rates. It is also found that the temperature gradients in the wax mounting have a negative effect on the flatness

4MOST-4-metre Multi-Object Spectroscopic Telescope

4MOST is a wide-field, high-multiplex spectroscopic survey facility under development for the VISTA telescope of the European Southern Observatory (ESO). Its main science drivers are in the fields of galactic archeology, high-energy physics, galaxy evolution and cosmology. 4MOST will in particular provide the spectroscopic complements to the large area surveys coming from space missions like Gaia, eROSITA, Euclid, and PLATO and from ground-based facilities like VISTA, VST, DES, LSST and SKA. The 4MOST baseline concept features a 2.5 degree diameter field-of-view with similar to 2400 fibres in the focal surface that are configured by a fibre positioner based on the tilting spine principle. The fibres feed two types of spectrographs; similar to 1600 fibres go to two spectrographs with resolution R> 5000 (lambda similar to 390-930 nm) and similar to 800 fibres to a spectrograph with R> 18,000 (lambda similar to 392-437 nm & 515-572 nm & 605-675 nm). Both types of spectrographs are fixed-configuration, three-channel spectrographs. 4MOST will have an unique operations concept in which 5 year public surveys from both the consortium and the ESO community will be combined and observed in parallel during each exposure, resulting in more than 25 million spectra of targets spread over a large fraction of the southern sky. The 4MOST Facility Simulator (4FS) was developed to demonstrate the feasibility of this observing concept. 4MOST has been accepted for implementation by ESO with operations expected to start by the end of 2020. This paper provides a top-level overview of the 4MOST facility, while other papers in these proceedings provide more detailed descriptions of the instrument concept[1], the instrument requirements development[2], the systems engineering implementation[3], the instrument model[4], the fibre positioner concepts[5], the fibre feed[6], and the spectrographs[7]