[tel-00726959, v1] CaractÃ©riser le milieu interstellaire ... - HAL - INRIA

More documents

Recommendations

Info

IRAM-30m EMIR time/sensitivity estimator3. on-the-fly observationsIRAM-30m EMIR time/sensitivity estimator3. on-the-fly observations• Finally, the total time spent on and off is given byStep #3: Computation of derived quantitiestel-00726959, version 1 - 31 Aug 2012tonoff = ncover nsubmap (n on/off t coveron + t coveroff ). (32)Using Eqs. 23 and 29, we derive()1tonoff = ncover tsubmap nsubmap 1 + √ . (33)non/offBoth t beamsig and tonoff are proportional to ncover tsubmap (cf. Eqs. 31 and 33). It is thus easy to derive thattonoff = t beamsigUsing Eq. 27, we can replace n on/off and obtainUsing Eqs. 5, 4 and 35, we obtain( √ ) 2nsubmap 1 + non/off . (34)tonoff = t beam (√sig nsubmap + √ ) 2nbeam . (35)(√ nbeam + √ )nsubmap Tsysσpsw = √ηspec dν npol ηtel ttel. (36)The last equation in theory enables us to find the rms noise as a function of the elasped telescope time(sensitivity estimation) and vice-versa (time estimation). However, it is not fully straightforward becausewe must enforce that ncover and nsubmap have an integer value.3.3.3 Time/Sensitivity estimationThis paragraph describes the algorithm to do a time/sensitivity estimation for a position-switched On-The-Fly observation.Step #1: Computation of nbeam and nsubmapnbeam is just computed as the ratio Amap/Abeam. Using Eqs. 28 and 25, we obtainnsubmap =Amap. (37)v area tsubmapUsing this equation, we start to compute nsubmap for tsubmap = tstable and v area = v maxarea. We want toenforce the integer character of nsubmap in a way which decreases the product tsubmap v area . To dothis, we usensubmap = 1 + int(nsubmap). (38)Eq. 38 ensures that tsubmap v area < tstable v maxarea. The value of v area must be decreased so that Eq. 37is enforced.Step #2: Computation of ttel or σ We use the following equations in descending order to computethe elapsed telescope time and in ascending order to compute the rms noise level:IRAM-30m EMIR time/sensitivity estimator1. t beamsigTsys2 , (39)=ηspec 2 σ 2 dν npol2. tonoff = t beam (√sig nsubmap + √ ) 2nbeam , (40)3. ηtel ttel = tonoff. (41)84. acknowledgementMoreover, σpsw/σfsw ≃ 0.84 for n on/off = 30, and ≃ 0.78 for n on/off = 100. Using eqs. 28 and 26, we seethat the limit on the maximum number of on per off is set bytstablen on/off =Abeam/vareamax , (50)i.e. the ratio of the maximum system stability time by the minimum time required to map a telescopebeam.As for tracked observations, there are other considerations to be taken into account. For extra-galacticobservations, the lines are large which excludes the use of frequency switched observations. For Galacticobservations, the intrinsic sensitivity of the receivers may make it difficult to find a closeby position devoidof signal. We can still use the position switched OTF observing mode. But we then have to observethe off position in frequency switched track observing mode long enough to be able to add back the offastronomical signal.4 AcknowledgementThe author thanks M. Guélin, S. Guilloteau, C. Kramer and C. Thum for useful discussions.ReferencesBall, J. A., in Meth. Exper. Phys., Vol. 12, Part C, Astrophysics: Radio Observations, Chap. 4.3, p. 46,ed. M. L. Meeks1. n on/off = nbeam , (42)nsubmap2. ncover = tbeam sigtsubmap(non/off + √ n on/off), (43)3. t beam ncover tsubmapon =n on/off(44)3. t beamoff= t beamon√ non/off. (45)Step #4: Is ncover an integer number? The interpretation of the above equation to compute ncoverhas two cases.1. ncover < 1. This means that either the user tries to cover a too large sky area in the giventelescope elasped time (sensitivity estimation) or the telescope need a minimum time to coverAmap at the maximum velocity possible with the telescope and this minimum time implies amore sensitive observation than requested by the user (time estimation).2. ncover ≥ 1. ncover will generally not be an integer, we can think to decrease tsubmap from tstableto obtain an integer value. However, this must be done at constant Asubmap(= v area tsubmap).Decreasing tsubmap thus implies increasing v area . It is not clear that this is possible because ofthe constraint v area < varea. max Another way to deal with this is to keep tsubmap to its maximumvalue and to adjust ttel (sensitivity estimation) or tsig and thus σ (time estimation) to obtain aninteger value of ncover. However, this implies a change in the wishes of the user. The programcan not make such a decision alone and we will only warn the user. Indeed, the worst case iswhen ncover is changing from 1 to 2 because this can decrease the sensitivity by a factor 1.4(sensitivity estimation) or double the elapsed telescope time (time estimation). The larger thevalue of ncover the less harm it is to enforce the integer character of ncover.3.4 ComparisonContrary to tracked observations, the position switched observing mode can be more efficient than thefrequency switched observing mode. Indeed, in frequency switch, the same time is spent in the on and offspectrum. When subtracting them, the off brings as much noise as the on. In position switch, the sameoff can be shared between many ons, in which case the optimal integration time on the off is much largerthan on each independent on spectrum. Hence, the noise brought by the off spectrum can be much smallerthan the noise brought by the on spectrum.For frequency switched observations,√ 2 nbeam Tsysσfsw =, (46)ηspec√dν npol ηtel ttelwhile for position switched observations,(√ nbeam + √ )nsubmap Tsysσpsw = √ηspec dν npol ηtel ttel. (47)We thus haveσpsw= 1 √ nsubmap√(1 +σfsw 2 nbeamPosition switched OTF is more efficient than frequency switched OTF forIRAM-30m EMIR time/sensitivity estimatorANumerical values). (48)nbeam1= n on/off ≥nsubmap3 − 2 √ ∼ 6. (49)29A. numerical valuesThis appendix groups all the numerical values used in the time/sensitivity estimator. We made conservativechoices for two reasons: 1) time/sensitivity estimators tend to be too optimistics and 2) EMIR is a newgeneration of receivers which had not yet been tested at the telescope.A.1 Overheads• ηtel = 0.5.• After estimating the number of tunings needed to complete the project, the user has to add to thetelescope time 30 minutes per tuning (this includes the observation of a line calibrator).A.2 Atmosphere• Tatm = 250 K.• The opacities at signal frequencies are computed with a recent version of the ATM program (maintainedby J.R. Pardo).• They are computed for 3 different amount of water vapor per season (1, 2 and 4 mm for the winterseason and 2, 4 and 7 mm for the summer season).A.3 Telescope• Tcab = 290 K.• Feff = 0.95 at 3 mm, 0.93 at 2 mm, 0.91 at 1 mm and 0.88 at 0.8 mm.A.4 FrontendsWarning: Please do not quote these values in your papers. You should refer to the publications whichfully describe the receivers.• The receiver temperature is the sum of– The mixer temperature: Typically 50 K below 260 GHz and 70 K above;– The mirror losses: Typically 10 K;– The dichroic losses: Typically 15 K. Nota Bene: Dichroics enable dual frequency observationby frequency separation of the sky signal.We end up with Trec = 75 K below 260 GHz and T rec = 95 K above 260 GHz.• Gim = 0.1.A.5 Backends• ηspec = 0.87 because of the 2 bit quantization at the input of the correlators.• The noise equivalent bandwidth of our correlators is almost equal to the channel spacing. So we donot take this into account in our estimation.1011
IRAM-30m EMIR time/sensitivity estimatorA. numerical valuesIRAM-30m EMIR time/sensitivity estimatorB. optimal number of on per off measurementsA.6 On-The-Fly• tstable = 2 minutes.• θ = 2460′′ν GHz .• The maximum linear velocity is limited by the maximum dumping rate of fdump = 2 Hz. We knowthat in order to avoid beam elongation along the scanning direction, we need to sample at least 4points per beam in the scanning direction. We thus end up withandv maxarea = fdumpv maxlinear = fdumpθarcsec/s (51)4θ θ2.5 4 arcsec2 /s or varea max θ 2= fdump10 arcsec2 /s (52)BOptimal number of ON per OFF measurementsThis section is just a reformulation of the original demonstration by Ball (1976).Let’s assume that we are measuring n on/off independent on-positions for a single off. The same integrationtime (ton) is spent on each on-position and the off integration time istoff = α ton, (53)where α can be varied. Using eq. 2 and tonoff = n on/offton + toff = (n on/off + α) ton, it can be shown thanT 2 (systonoff =ηspec 2 σ 2 dνDifferenciating with respect to α, we obtain1 + n on/off + α + n on/offα). (54)dtonoffdα∝ 1 − n on/offα 2 (55)Setting the result to zero then gives that the minimum elapsed time to reach a given rms noise is obtainedforα = √ n on/off or t optimaloff = √ n on/off ton. (56)tel-00726959, version 1 - 31 Aug 20121213
Page 1 and 2:
UNIVERSITÉ PIERRE ET MARIE CURIEHA
Page 3 and 4:
tel-00726959, version 1 - 31 Aug 20
Page 5 and 6:
Table des matières1 Rapport de sou
Page 7 and 8:
Rapport après soutenanceHabilitati
Page 9 and 10:
Chapitre 2Curriculum vitaetel-00726
Page 11 and 12:
2.7 ANIMATION ET DIFFUSION DE LA CU
Page 13 and 14:
2.8 PARCOURS 131992-1993 ÉCOLE NOR
Page 15 and 16:
Chapitre 3Copyright: IRAM/PdBIIntro
Page 17 and 18:
tel-00726959, version 1 - 31 Aug 20
Page 19 and 20:
4.2 ETUDES DIRECTES EN ÉMISSION 19
Page 21 and 22:
4.4 LA LUMINOSITY CO PAR MOLÉCULE
Page 23 and 24:
356 E. Falgarone et al.: Extreme ve
Page 25 and 26:
Page 27 and 28:
Page 29 and 30:
Page 31 and 32:
Page 33 and 34:
Page 35 and 36:
Page 37 and 38:
A&A 518, A45 (2010)1001010⌠⌡ τ
Page 39 and 40:
A&A 518, A45 (2010)If X HCO + is as
Page 41 and 42:
A&A 518, A45 (2010)tel-00726959, ve
Page 43 and 44:
A&A 518, A45 (2010)tel-00726959, ve
Page 45 and 46:
A&A 518, A45 (2010)Table E.2. Data
Page 47 and 48:
A&A 541, A58 (2012)tel-00726959, ve
Page 49 and 50:
A&A 541, A58 (2012)tel-00726959, ve
Page 51 and 52:
A&A 541, A58 (2012)0.08 0.10.20.12
Page 53 and 54:
A&A 541, A58 (2012)b=240.11 0.1 0.1
Page 55 and 56:
0.080.09 0.1A&A 541, A58 (2012)0.14
Page 57 and 58:
A&A 541, A58 (2012)43˚00'0.3 0.44
Page 59 and 60:
A&A 541, A58 (2012)68˚00'1.1 0.91.
Page 61 and 62:
A&A 541, A58 (2012)α(J2000)-19H57m
Page 63 and 64:
A&A 541, A58 (2012)tel-00726959, ve
Page 65 and 66:
A&A 541, A58 (2012)Jenkins, E. B.,
Page 67 and 68:
A&A 541, A58 (2012)Galactic Latitud
Page 69 and 70:
tel-00726959, version 1 - 31 Aug 20
Page 71 and 72:
5.2 UNE PHYSIQUE BIEN CONTRAINTE ET
Page 73 and 74:
5.3 PERSPECTIVES : DES RELEVÉS DE
Page 75 and 76:
A&A 435, 885-899 (2005)DOI: 10.1051
Page 77 and 78:
tel-00726959, version 1 - 31 Aug 20
Page 79 and 80:
J. Pety et al.: Are PAHs precursors
Page 81 and 82:
Page 83 and 84:
Page 85 and 86:
Page 87 and 88:
Page 89 and 90:
Page 91 and 92:
566 J. R. Goicoechea et al.: Low su
Page 93 and 94:
Page 95 and 96:
Page 97 and 98:
Page 99 and 100:
Page 101 and 102:
Page 103 and 104:
Page 105 and 106:
Page 107 and 108:
tel-00726959, version 1 - 31 Aug 20
Page 109 and 110:
J. R. Goicoechea et al.: Low sulfur
Page 111 and 112:
L42J. Pety et al.: Deuterium fracti
Page 113 and 114:
L44J. Pety et al.: Deuterium fracti
Page 115 and 116:
772 J. R. Goicoechea et al.: The io
Page 117 and 118:
Page 119 and 120:
Page 121 and 122:
Page 123 and 124:
Page 125 and 126: 782 J. R. Goicoechea et al.: The io
Page 127 and 128: A&A 494, 977-985 (2009)DOI: 10.1051
Page 129 and 130: M. Gerin et al.: HCO mapping of the
Page 137 and 138: Table 1. Observation parameters for
Page 139 and 140: A&A 534, A49 (2011)tel-00726959, ve
Page 145 and 146: tel-00726959, version 1 - 31 Aug 20
Page 157 and 158: ¡¢£¤¥¢¦¢ §¨ ©
Page 161 and 162: 7.2 MODE INTERFÉROMÉTRIQUE 161tel
Page 163 and 164: 7.3 LE FUTUR DE LA RADIO-ASTRONOMIE
Page 165 and 166: CLASS evolution: I. Improved OTF su
Page 167 and 168: CLASS evolution: I. Improved OTF su
Page 169 and 170: A&A 526, A47 (2011)DOI: 10.1051/000
Page 171 and 172: S. Maret et al.: Weeds: a CLASS ext
Page 173 and 174: S. Maret et al.: Weeds: a CLASS ext
Page 175: IRAM-30m EMIR time/sensitivity esti
Page 179 and 180: IRAM-30m HERA time/sensitivity esti
Page 181 and 182: ¬þ«ðZñÛùþ˜ï³þ«ðWMõÑ
Page 183 and 184: ¨-A¨-, #f¡§¨\¤qŠ’‹¼€(
Page 185 and 186: ¤H F!";
Page 187 and 188: #O.u\J0$!&%©ÉQ©6¦©¨-.u& (HÌ>
Page 189 and 190: ¨*.G©6E¦cÇ¦©¨&ẗØn¨"!-‡
Page 191 and 192: ¢¡¤£¦¥¨§ P© ¡ £¦¥¨§
Page 193 and 194: '¥0vB"(-7£O.'¥!5#&(-7)7)(:9.*d#J
Page 195 and 196: ¥¤¡ b@‚¥_ƒO@02,.(-EFJbe O@#V
Page 197 and 198: 02J$#J+'10-ï 3 02EFJ+')EKJ5L5†R(
Page 217 and 218: Table C.1. Definition of the symbol
Page 219 and 220: IRAM Memo 2011-2WIFISYN:The GILDAS
Page 221 and 222: WIFISYN3. practiceWIFISYN3. practic
Page 223 and 224: WIFISYNA. implementation planWIFISY
Page 227 and 228:
8.3 PERSPECTIVES 227tel-00726959, v
Page 229 and 230:
3 REQUIREMENTS 44 CHANGES FOR END-U
Page 231 and 232:
5 CHANGES FOR PROGRAMMERS 125 CHANG
Page 233 and 234:
A EXHAUSTIVE DESCRIPTION OF THE CHA
Page 235 and 236:
Chapitre 9Copyright: Stéphane Guis
Page 237 and 238:
9.3 ACTIVITÉS 2008-2011 237tel-007
Page 239 and 240:
Contribution de l'Action Spécique
Page 241 and 242:
A. des multi-pixels à bure : une s
Page 243 and 244:
5. besoins en services annexes, bé
Page 245 and 246:
Articles publiés dans des revues
Page 247 and 248:
ARTICLES PUBLIÉS DANS DES REVUES
Page 249 and 250:
Mémos IRAM et ALMAtel-00726959, ve
Page 251 and 252:
Actes de colloques nationaux et int
Page 253 and 254:
ACTES DE COLLOQUES NATIONAUX ET INT
Page 255 and 256:
tel-00726959, version 1 - 31 Aug 20
show all

[tel-00726959, v1] CaractÃ©riser le milieu interstellaire ... - HAL - INRIA

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?