ContactThe Argus System in Contact• How many telescopes?• How many channels?• Channel Width?• Sensitivity?ARGUS131 telescopes pg. 63Built by expanding the VLAif similar antennas: 131 ~ 5 × the area 27Coverage: 109 channels pg. 56, 62channel width < 1 Hz pg. 56⇒ ~ 109 Hz if width = 1 HzSensitivity: if assume better than VLA by 5,5 Jy in 1 sec5 × 10-26 W m-2 Hz-1The Signal• Frequency at which it was first detected?• Bandwidth?• Polarization?• Other frequencies?The SignalFirst detected near 9 GHz pg. 66ν = 9.24176684 pg. 72Δν = 430 HzLinearly polarized pg. 66Later found at 1.420 GHz H pg. 78 1.667 GHz OHBimodal pulses 179 and 174 Jy pg. 72Source of Signal• How was terrestrial interference ruled out?• How was it determined to come from Vega?• How do we know it was intended for us?– Rather than omnidirectional– BEFORE the message decodedThe SignalNot Terrestrial:Moving Sidereally pg. 66VEGA:Interferometric Position pg. 65Proper Motion pg. 78Doppler Corrected pg. 78What were the 4 Levels of information?• How encoded (modulation method)?• What was the purpose of each?The Prime NumbersAmplitude Modulation- (“Strength is the Message”)Bimodal amplitudes 174 & 179 JyTime0179 174Convention179 = 1174 = 0 1 1 1 0 1 1 25 + 24 + 23 + 0 + 21 + 1 32 + 16 + 8 + 0 + 2 + 1 = 59 (pg. 68)The Movie (and the Instructions)Polarization Modulation (pg. 83)- (“Direction is the Message”)Linear Pol.Vertical Pol.Horizontal Pol.Circular (or Elliptical) PolarizationRight-handedDecoding the Movie• Repeating pattern• Tens of billions of bits• Product of 3 prime numbers• Guess 2D image and time, so movie• Purpose?– They know about us…Machine Instructions• Palimpsest (pg. 100)• Under the movie (pg. 185)• Polarization modulation• Purpose:Suggestions for the Primer• Sol Hadden made 5 suggestions for finding it• What were they?• Which was right?Five Suggestions (pg. 220)• Slower bit rate (e.g., 1 bit per hour)• Faster bit rates (would require more BW)• Occasional fast data dump• Phase modulation• Have to detect from space– e.g., around 5 mm, where O2 blocks wavesThe PrimerPhase Modulation- (“Timing is the Message”)Steadily IncreasingPhaseRapid Changes in PhaseHow The Primer Works1 A 1 B 2 Z 1 + 1 = 2 TRUE1 A 2 B 3 Z 1 + 2 = 3 TRUE1 A 2 B 4 Y 1 + 2 = 4 FALSE⇒ A is +B is =Z is TRUEY is
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