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2.5 Gratings

Six gratings are presently available at the coudé spectrograph and their specifications are given in table 5. Gratings used with the 4 m RC spectrograph may also be requested in advance for use with CCDs to yield lower resolutions. Table 6 lists the specifications of the RC gratings.

The grating tilt for a particular camera and wavelength may be set by using the grating control window on the telescope control computer terminal (§7.2). Note that the grating drive stepper-motor power supply switches, located on the slit-head control panel (AC power), and the observing room rack panel, must both be turned on in order for the grating drive to function. The setting accuracy of the stepper-motor varies from about 1 to 5 Å depending upon the grating and order, although there may be an offset due to camera realignment or different CCD. The power switch in the observing room should be turned off after setting to insure against possible motion.

If using third order with grating A or B, interference from 4th order may be a problem at some wavelengths. Use of the echelle grating requires a grism cross disperser (Table 7) or narrow band filter to isolate the order of interest. Table 8 and table 9 are lists of echelle orders, central wavelengths, and dispersions for the echelle grating on cameras 5 and 6. Figure 3 shows the relation between order separation and grism distance below the slit for the various grisms and the 31.6 g/mm echelle. The spectral coverage between the highest and lowest orders varies from roughly 1500Å for the grisms used in first order, to 700Å in second order. Plots for each grism are kept in a notebook at the spectrograph.

NOTE: ALL grating changes should be done only by technical assistants or instrument assistants. Care must be used in locating grisms to avoid the region from 48 to 70 inches below the slit. In this region, collisions between the grating cell holder and the grism can occur.


 

Table 5: Coude spectrograph gratings


 

Table 6: RC grating use on coude spectrograph


 

Table 7: Cross dispersing grisms


  

Figure 3: Order Separations for 31.6 g/mm Echelle.


Order Blaze(A) FSR Recip. Disp. Order Blaze(A) FSR Recip. Disp.
55. 10228. 186. 2.92 116. 4850. 42. 1.38
56. 10046. 179. 2.86 117. 4808. 41. 1.37
57. 9869. 173. 2.81 118. 4767. 40. 1.36
58. 9699. 167. 2.77 119. 4727. 40. 1.35
59. 9535. 162. 2.72 120. 4688. 39. 1.34
60. 9376. 156. 2.67 121. 4649. 38. 1.33
61. 9222. 151. 2.63 122. 4611. 38. 1.31
62. 9074. 146. 2.59 123. 4574. 37. 1.30
63. 8929. 142. 2.55 124. 4537. 37. 1.29
64. 8790. 137. 2.51 125. 4500. 36. 1.28
65. 8655. 133. 2.47 126. 4465. 35. 1.27
66. 8524. 129. 2.43 127. 4430. 35. 1.26
67. 8396. 125. 2.39 128. 4395. 34. 1.25
68. 8273. 122. 2.36 129. 4361. 34. 1.24
69. 8153. 118. 2.32 130. 4327. 33. 1.23
70. 8037. 115. 2.29 131. 4294. 33. 1.22
71. 7923. 112. 2.26 132. 4262. 32. 1.22
72. 7813. 109. 2.23 133. 4230. 32. 1.21
73. 7706. 106. 2.20 134. 4198. 31. 1.20
74. 7602. 103. 2.17 135. 4167. 31. 1.19
75. 7501. 100. 2.14 136. 4136. 30. 1.18
76. 7402. 97. 2.11 137. 4106. 30. 1.17
77. 7306. 95. 2.08 138. 4077. 30. 1.16
78. 7212. 92. 2.06 139. 4047. 29. 1.15
79. 7121. 90. 2.03 140. 4018. 29. 1.15
80. 7032. 88. 2.01 141. 3990. 28. 1.14
81. 6945. 86. 1.98 142. 3962. 28. 1.13
82. 6860. 84. 1.96 143. 3934. 28. 1.12
83. 6778. 82. 1.93 144. 3907. 27. 1.11
84. 6697. 80. 1.91 145. 3880. 27. 1.11
85. 6618. 78. 1.89 146. 3853. 26. 1.10
86. 6541. 76. 1.87 147. 3827. 26. 1.09
87. 6466. 74. 1.84 148. 3801. 26. 1.08
88. 6393. 73. 1.82 149. 3776. 25. 1.08
89. 6321. 71. 1.80 150. 3750. 25. 1.07
90. 6251. 69. 1.78 151. 3726. 25. 1.06
91. 6182. 68. 1.76 152. 3701. 24. 1.06
92. 6115. 66. 1.74 153. 3677. 24. 1.05
93. 6049. 65. 1.72 154. 3653. 24. 1.04
94. 5985. 64. 1.71 155. 3629. 23. 1.03
95. 5922. 62. 1.69 156. 3606. 23. 1.03
96. 5860. 61. 1.67 157. 3583. 23. 1.02
97. 5800. 60. 1.65 158. 3560. 23. 1.02
98. 5740. 59. 1.64 159. 3538. 22. 1.01
99. 5682. 57. 1.62 160. 3516. 22. 1.00
100. 5626. 56. 1.60 161. 3494. 22. 1.00
101. 5570. 55. 1.59 162. 3473. 21. 0.99
102. 5515. 54. 1.57 163. 3451. 21. 0.98
103. 5462. 53. 1.56 164. 3430. 21. 0.98
104. 5409. 52. 1.54 165. 3409. 21. 0.97
105. 5358. 51. 1.53 166. 3389. 20. 0.97
106. 5307. 50. 1.51 167. 3369. 20. 0.96
107. 5258. 49. 1.50 168. 3349. 20. 0.95
108. 5209. 48. 1.49 169. 3329. 20. 0.95
109. 5161. 47. 1.47 170. 3309. 19. 0.94
110. 5114. 46. 1.46 171. 3290. 19. 0.94
111. 5068. 46. 1.45 172. 3271. 19. 0.93
112. 5023. 45. 1.43 173. 3252. 19. 0.93
113. 4978. 44. 1.42 174. 3233. 19. 0.92
114. 4935. 43. 1.41 175. 3215. 18. 0.92
115. 4892. 43. 1.39 176. 3196. 18. 0.91


Table 8: 31.6 g/mm, 63 echelle grating parameters for camera 5


Order Blaze(A) FSR Recip. Disp. Order Blaze(A) FSR Recip. Disp.
55. 10247. 186. 0.83 116. 4863. 42. 0.39
56. 10064. 179. 0.81 117. 4821. 41. 0.39
57. 9888. 173. 0.80 118. 4781. 40. 0.39
58. 9717. 167. 0.79 119. 4740. 40. 0.38
59. 9553. 162. 0.77 120. 4701. 39. 0.38
60. 9393. 156. 0.76 121. 4662. 38. 0.38
61. 9239. 151. 0.75 122. 4624. 38. 0.37
62. 9090. 146. 0.74 123. 4586. 37. 0.37
63. 8946. 142. 0.72 124. 4548. 37. 0.37
64. 8806. 137. 0.71 125. 4513. 36. 0.36
65. 8671. 133. 0.70 126. 4477. 35. 0.36
66. 8540. 129. 0.69 127. 4442. 35. 0.36
67. 8412. 125. 0.68 128. 4407. 34. 0.36
68. 8288. 122. 0.67 129. 4373. 34. 0.35
69. 8168. 118. 0.66 130. 4339. 33. 0.35
70. 8052. 115. 0.65 131. 4306. 33. 0.35
71. 7938. 112. 0.64 132. 4273. 32. 0.34
72. 7828. 109. 0.63 133. 4241. 32. 0.34
73. 7721. 106. 0.62 134. 4210. 31. 0.34
74. 7616. 103. 0.62 135. 4179. 31. 0.34
75. 7515. 100. 0.61 136. 4148. 30. 0.33
76. 7416. 97. 0.60 137. 4118. 30. 0.33
77. 7320. 95. 0.59 138. 4088. 30. 0.33
78. 7226. 92. 0.58 139. 4058. 29. 0.33
79. 7134. 90. 0.58 140. 4029. 29. 0.32
80. 7045. 88. 0.57 141. 4001. 28. 0.32
81. 6958. 86. 0.56 142. 3973. 28. 0.32
82. 6873. 84. 0.56 143. 3945. 28. 0.32
83. 6790. 82. 0.55 144. 3917. 27. 0.32
84. 6710. 80. 0.54 145. 3890. 27. 0.31
85. 6631. 78. 0.54 146. 3864. 26. 0.31
86. 6554. 76. 0.53 147. 3837. 26. 0.31
87. 6478. 74. 0.52 148. 3811. 26. 0.31
88. 6405. 73. 0.52 149. 3786. 25. 0.31
89. 6333. 71. 0.51 150. 3761. 25. 0.30
90. 6262. 69. 0.51 151. 3733. 25. 0.30
91. 6194. 68. 0.50 152. 3708. 24. 0.30
92. 6126. 66. 0.50 153. 3684. 24. 0.30
93. 6060. 65. 0.49 154. 3660. 24. 0.30
94. 5996. 64. 0.49 155. 3636. 23. 0.29
95. 5933. 62. 0.48 156. 3613. 23. 0.29
96. 5871. 61. 0.48 157. 3590. 23. 0.29
97. 5810. 60. 0.47 158. 3567. 23. 0.29
98. 5751. 59. 0.47 159. 3545. 22. 0.29
99. 5693. 57. 0.46 160. 3523. 22. 0.28
100. 5636. 56. 0.46 161. 3501. 22. 0.28
101. 5585. 55. 0.45 162. 3479. 21. 0.28
102. 5530. 54. 0.45 163. 3458. 21. 0.28
103. 5477. 53. 0.44 164. 3437. 21. 0.28
104. 5424. 52. 0.44 165. 3416. 21. 0.28
105. 5372. 51. 0.43 166. 3395. 20. 0.27
106. 5322. 50. 0.43 167. 3375. 20. 0.27
107. 5272. 49. 0.43 168. 3355. 20. 0.27
108. 5223. 48. 0.42 169. 3335. 20. 0.27
109. 5175. 47. 0.42 170. 3315. 19. 0.27
110. 5128. 46. 0.41 171. 3296. 19. 0.27
111. 5082. 46. 0.41 172. 3277. 19. 0.26
112. 5037. 45. 0.41 173. 3258. 19. 0.26
113. 4992. 44. 0.40 174. 3239. 19. 0.26
114. 4948. 43. 0.40 175. 3221. 18. 0.26
115. 4905. 43. 0.40 176. 3202. 18. 0.26

Table 9: 31.6 g/mm, 63 echelle grating paramters for camera 6


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