0 Assigned ID: 609 ----- Attempting Submission 1 (Fri Apr 05 18:25:04 GMT 2019) ----- HST Phase I Proposal 609 (proposalTOn.apt) successfully submitted. Receipt: # 609-1 ----- Attempting Submission 2 (Fri Apr 05 21:51:13 GMT 2019) ----- HST Phase I Proposal 609 (proposalTOn.apt) successfully submitted. Receipt: # 609-2 ----- Attempting Submission 3 (Sat Apr 06 10:35:21 GMT 2019) ----- HST Phase I Proposal 609 (proposalTOn.apt) successfully submitted. Receipt: # 609-3 Version 2, 23/07/2019, no ORIENT constraint -813867189 ----- Attempting Submission 1 (Fri Jul 19 15:14:39 GMT 2019) ----- HST Phase II Proposal 15945 (proposalTOn.apt) successfully submitted. Receipt: # 15945-1 ----- Attempting Submission 2 (Tue Jul 23 10:31:34 GMT 2019) ----- This is a two-orbits proposal to explore pre-main sequence (pre-MS) stars in Large Magellanic Cloud young clusters to assess, once and for all, if multiple bursts of star formation can be supported by these systems. The discovery that nearly all star clusters younger than 2Gyr in both Magellanic Clouds exhibit double/extended main-sequence turn offs (eMSTOs) has been one of the major advances made by HST in stellar astrophysics. Despite a huge effort has been undertaken to understand these observations, the mechanism responsible for the eMSTO is still controversial. It has been suggested that the eMSTO is due to coeval stellar populations with different rotation, but it seems that rotation alone is not able to reproduce the eMSTOs. On the other hand, the eMSTO could be due to a spread in age, so that these clusters would be the younger counterparts of old globular clusters with multiple populations. We propose a novel approach to disentangle between age and rotation by using the Turn-On (TOn), where the pre-MS reaches the main sequence in the color-magnitude diagram (CMD). The most remarkable feature introduced by different ages on this region of the CMD would be the appearance of multiple or broaden TOn peaks in the luminosity function. Specifically a single narrow peak is expected in the case of a single generation, whereas multiple/broaden TOn peaks would imply multiple stellar generations. The proposed observations will allow us, to understand, whether the age spread contributes to eMSTO in young clusters or not, and will be surely seminal for future investigation of the still-eluding multiple stellar populations phenomenon. We plan deep photometry to reach a S/N of about 50, at a magnitude of 24.0 in the F814W band and study the luminosity function (LF). Since deep observations are needed to well sample the LF and the CMD at the faintest magnitudes, we need filters that provide a high S/N in a limited exposure time, and the F606W and F814W filters fulfill exactly these requirements. According to the WFC3 Exposure Time Calculator (ETC), to reach a S/N sim 50, needed for our goal, at a magnitude of 24.0 in the F814W band we need an exposure time of at least 3000 seconds. On the other hand, the F606W requires a shorter exposure time to reach the same S/N. To achieve the desired S/N we, therefore, need a total of two orbits. We plan to observe NGC 1818 for 2268 seconds (724s+772s+772s) and 2400 seconds (795s+795s+810s) in the F606W and F814W respectively. All exposures will be optimally dithered to ensure the best possible photometric accuracy. We request therefore a total of only two orbits. Parallel fields will be taken through the WFC/ACS F606W for a total of 1820 seconds (560s+630s+630s) and F814W, for 1990 seconds (650s+690s+650s). They will serve the purpose of field decontamination, allowing us to subtract non-cluster members in our cluster field. Specifically, the statistical subtraction technique exploits the comparison of the color-magnitude diagram in the cluster field with that of a reference field. Data reduction Photometry and astrometry will be derived with the software developed by Jay Anderson for ACS/WFC and WFC3/UVIS cameras. Reduced Gyro Mode (RGM) operations According to the report ''Science Implications of Operating HST Reduced Gyro Mode'' of May 6th, the largest science imparts of operating in RGM is the reduction in the number of orbits per week (from ~84/week to ~73/week), and a longer search time for the ''Target acquisition'', with a consequent reduction of the science observing time during visibility periods by ~ 120 seconds. Given these premises, operating in RGM will have a non-negligible impact on our observations, nonetheless, they will provide the required accuracy to reach our scientific goal. In the last years members of our team have revolutionized our knowledge of stellar populations in young clusters. Our scientific expertise ranges from photometry, to spectroscopy and theoretical modeling of both old and star forming stellar systems. We therefore have all the necessary tools and capabilities to exploit at best this data to understand, once and for all, the phenomenon of multipopulations in young clusters. This will provide crucial insights about highly debated phenomenon of mulitple stellar populations in old Galactic globular clusters. A.P. Milone and E.P. Lagioia have long experience in photometric and astrometric data analysis. They exploit state-of-the-art data-reduction and data-analysis techniques to address the phenomenon of multiple stellar populations in young and old globular clusters. A. F. Marino possesses excellent skills in the spectral analysis. She has given a fundamental contribution to the characterisation of multiple stellar populations in young clusters, both Galactic and extra-Galactic. M. Tailo and M. Cignoni are experts in stellar evolution and theoretical models. G. Cordoni is Ph.D. student, working on multiple stellar populations in young and old stellar clusters. This dataset will be of fundamental importance for his Ph.D. thesis. Stellar Populations 6 false false false false false false false SUPPORTED EXT-CLUSTER GLOBULAR CLUSTER This object was generated by the target selector and retrieved from the SIMBAD database. J2000 J2000 WFC3/UVIS Imaging No No F606W WFC3/UVIS Imaging No No F814W ACS/WFC Imaging No No F606W ACS/WFC Imaging No No F814W 1563870784197 The scheduling data was generated by CASM 27.2. CASM was run in Phase II mode. /home/cordoni/Scrivania/PHD/Proposals/TurnOnGiacomo/HSTAPT/OP-cache/proposalTOn-v01.xml NGC-1818 (Tic-Visit :proposal-id 15945 :visit-id "01" :proposal-version -1 :trans-version "20190514" :date "23-Jul-2019 10:33:03.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 3437824 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 15945 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 15945 :visit-id "01" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2637 :al-overhead-at-end 116 :internal-dur-at-end 668 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2970 :pcs-gap 0 ) (Tic-Orbit :proposal-id 15945 :visit-id "01" :orbit-number 2 :pcs-time 302 :si-vis-utilization 2668 :al-overhead-at-end 116 :internal-dur-at-end 1015 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2970 :pcs-gap 0 ) true 2 0