<table><caption>**Table 4.** Total column density derived by the summation of the individual interstellar components listed in Table 3. We also present the total derived by the AOD method, discussed in Section 3.4.</caption><thead><tr><th rowspan="2">Star</th><th rowspan="2">S/N</th><th colspan="2">Na I (3302.37)</th><th rowspan="2">S/N</th><th colspan="2">Na I (3302.98)</th><th rowspan="2">S/N</th><th colspan="2">Ti II (3383.76)</th><th rowspan="2">S/N</th><th colspan="2">Ca II (3393.66)</th><th rowspan="2">H I</th></tr><tr><th>log N (Prof)</th><th>log N (AOD)</th><th>log N (Prof)</th><th>log N (AOD)</th><th>log N (Prof)</th><th>log N (AOD)</th><th>log N (Prof)</th><th>log N (AOD)</th><th>log N (Prof)</th><th>log N (AOD)</th></tr></thead><tbody><tr><td>HD 164794</td><td>200</td><td>13.54 ± 0.03</td><td>13.49 ± 0.05</td><td>200</td><td>13.63 ± 0.03</td><td>13.55 ± 0.11</td><td>230</td><td>12.08 ± 0.06</td><td>12.10 ± 0.03</td><td>290</td><td>12.49 ± 0.03</td><td>12.59 ± 0.01</td><td>21.29 ± 0.07</td></tr><tr><td>HD 163800</td><td>260</td><td>13.84 ± 0.02</td><td>13.75 ± 0.01</td><td>260</td><td>13.98 ± 0.03</td><td>13.92 ± 0.03</td><td>320</td><td>12.04 ± 0.05</td><td>12.05 ± 0.02</td><td>580</td><td>12.61 ± 0.02</td><td>12.53 ± 0.01</td><td>–</td></tr><tr><td>HD 170235</td><td>210</td><td>13.57 ± 0.05</td><td>13.60 ± 0.03</td><td>210</td><td>13.58 ± 0.07</td><td>13.60 ± 0.07</td><td>220</td><td>12.06 ± 0.07</td><td>12.07 ± 0.03</td><td>300</td><td>12.67 ± 0.02</td><td>12.65 ± 0.01</td><td>–</td></tr><tr><td>HD 167264</td><td>260</td><td>13.52 ± 0.04</td><td>13.50 ± 0.05</td><td>260</td><td>13.53 ± 0.04</td><td>13.47 ± 0.09</td><td>290</td><td>11.98 ± 0.07</td><td>11.98 ± 0.03</td><td>–</td><td>–</td><td>–</td><td>21.14 ± 0.13</td></tr><tr><td>HD 171432</td><td>430</td><td>13.82 ± 0.03</td><td>13.83 ± 0.04</td><td>430</td><td>13.82 ± 0.04</td><td>13.82 ± 0.07</td><td>370</td><td>12.23 ± 0.04</td><td>12.23 ± 0.04</td><td>590</td><td>12.91 ± 0.02</td><td>12.89 ± 0.01</td><td>–</td></tr><tr><td>HD 169454</td><td>240</td><td>14.24 ± 0.04</td><td>14.17 ± 0.01</td><td>240</td><td>14.29 ± 0.04</td><td>14.23 ± 0.03</td><td>340</td><td>12.54 ± 0.03</td><td>12.53 ± 0.01</td><td>–</td><td>–</td><td>–</td><td>–</td></tr><tr><td>HD 188294</td><td>380</td><td>&lt;12.69</td><td>&lt;12.69</td><td>380</td><td>&lt;12.99</td><td>&lt;12.99</td><td>450</td><td>11.34 ± 0.11</td><td>11.28 ± 0.06</td><td>420</td><td>11.33 ± 0.05</td><td>11.32 ± 0.03</td><td>–</td></tr><tr><td>HD 30677</td><td>330</td><td>13.27 ± 0.04</td><td>13.26 ± 0.07</td><td>330</td><td>13.26 ± 0.04</td><td>13.29 ± 0.13</td><td>320</td><td>12.19 ± 0.07</td><td>12.19 ± 0.02</td><td>430</td><td>12.70 ± 0.02</td><td>12.68 ± 0.01</td><td>21.10 ± 0.09</td></tr><tr><td>HD 36861</td><td>330</td><td>13.22 ± 0.03</td><td>13.10 ± 0.08</td><td>330</td><td>13.18 ± 0.05</td><td>12.99 ± 0.11</td><td>340</td><td>11.74 ± 0.05</td><td>11.74 ± 0.03</td><td>370</td><td>12.50 ± 0.02</td><td>12.48 ± 0.01</td><td>20.81 ± 0.12</td></tr><tr><td>HD 37490</td><td>470</td><td>12.84 ± 0.09</td><td>12.86 ± 0.14</td><td>470</td><td>12.76 ± 0.17</td><td>12.72 ± 0.19</td><td>500</td><td>11.66 ± 0.06</td><td>11.67 ± 0.04</td><td>710</td><td>12.30 ± 0.01</td><td>12.30 ± 0.01</td><td>20.90 ± 0.06</td></tr><tr><td>HD 43285</td><td>220</td><td>&lt;12.63</td><td>&lt;12.63</td><td>220</td><td>&lt;12.94</td><td>&lt;12.94</td><td>280</td><td>11.41 ± 0.12</td><td>11.40 ± 0.06</td><td>430</td><td>12.02 ± 0.02</td><td>11.92 ± 0.01</td><td>–</td></tr><tr><td>HD 36646</td><td>330</td><td>&lt;12.44</td><td>&lt;12.44</td><td>330</td><td>&lt;12.75</td><td>&lt;12.75</td><td>400</td><td>11.58 ± 0.09</td><td>11.56 ± 0.04</td><td>470</td><td>12.22 ± 0.02</td><td>12.27 ± 0.01</td><td>–</td></tr><tr><td>HD 48099</td><td>330</td><td>13.40 ± 0.05</td><td>13.40 ± 0.03</td><td>330</td><td>13.36 ± 0.09</td><td>13.38 ± 0.06</td><td>410</td><td>12.11 ± 0.03</td><td>12.12 ± 0.01</td><td>–</td><td>–</td><td>–</td><td>21.20 ± 0.08</td></tr><tr><td>HD 37055</td><td>300</td><td>&lt;12.73</td><td>&lt;12.73</td><td>300</td><td>&lt;13.03</td><td>&lt;13.03</td><td>400</td><td>11.28 ± 0.09</td><td>11.34 ± 0.07</td><td>520</td><td>11.97 ± 0.03</td><td>11.97 ± 0.01</td><td>–</td></tr><tr><td>HD 33328</td><td>550</td><td>12.53 ± 0.12</td><td>12.36 ± 0.09</td><td>550</td><td>12.69 ± 0.20</td><td>12.63 ± 0.26</td><td>470</td><td>11.55 ± 0.08</td><td>11.54 ± 0.03</td><td>660</td><td>12.11 ± 0.01</td><td>12.11 ± 0.01</td><td>–</td></tr><tr><td>HD 45725</td><td>250</td><td>&lt;12.56</td><td>&lt;12.56</td><td>250</td><td>&lt;12.86</td><td>&lt;12.86</td><td>300</td><td>11.12 ± 0.18</td><td>11.11 ± 0.09</td><td>520</td><td>11.56 ± 0.03</td><td>11.54 ± 0.01</td><td>–</td></tr><tr><td>HD 52918</td><td>370</td><td>&lt;12.66</td><td>&lt;12.66</td><td>370</td><td>&lt;12.96</td><td>&lt;12.96</td><td>450</td><td>11.15 ± 0.16</td><td>11.16 ± 0.10</td><td>520</td><td>11.82 ± 0.03</td><td>11.96 ± 0.01</td><td>20.38 ± 0.09</td></tr><tr><td>HD 46185</td><td>310</td><td>&lt;12.52</td><td>&lt;12.52</td><td>310</td><td>&lt;12.82</td><td>&lt;12.82</td><td>350</td><td>11.61 ± 0.09</td><td>11.62 ± 0.03</td><td>550</td><td>12.24 ± 0.01</td><td>12.24 ± 0.01</td><td>–</td></tr><tr><td>HD 58343</td><td>250</td><td>13.29 ± 0.03</td><td>13.32 ± 0.03</td><td>250</td><td>13.31 ± 0.04</td><td>13.32 ± 0.05</td><td>320</td><td>11.38 ± 0.12</td><td>11.40 ± 0.04</td><td>410</td><td>12.07 ± 0.02</td><td>12.19 ± 0.01</td><td>–</td></tr><tr><td>HD 50896</td><td>250</td><td>12.50 ± 0.13</td><td>12.66 ± 0.42</td><td>250</td><td>12.38 ± 0.26</td><td>12.56 ± 0.55</td><td>260</td><td>12.05 ± 0.07</td><td>12.07 ± 0.05</td><td>300</td><td>12.47 ± 0.02</td><td>12.53 ± 0.01</td><td>20.54 ± 0.13</td></tr><tr><td>HD 58978</td><td>500</td><td>&lt;12.30</td><td>&lt;12.30</td><td>500</td><td>&lt;12.60</td><td>&lt;12.60</td><td>520</td><td>11.35 ± 0.05</td><td>11.28 ± 0.04</td><td>620</td><td>11.90 ± 0.03</td><td>11.91 ± 0.01</td><td>20.24 ± 0.10</td></tr><tr><td>HD 49131</td><td>350</td><td>&lt;12.59</td><td>&lt;12.59</td><td>350</td><td>&lt;12.89</td><td>&lt;12.89</td><td>620</td><td>11.31 ± 0.05</td><td>11.31 ± 0.05</td><td>770</td><td>11.98 ± 0.01</td><td>11.99 ± 0.01</td><td>–</td></tr><tr><td>HD 61429</td><td>260</td><td>&lt;12.26</td><td>&lt;12.26</td><td>260</td><td>&lt;12.56</td><td>&lt;12.56</td><td>270</td><td>11.11 ± 0.08</td><td>11.17 ± 0.05</td><td>520</td><td>10.89 ± 0.07</td><td>10.82 ± 0.03</td><td>–</td></tr><tr><td>HD 58377</td><td>300</td><td>&lt;12.34</td><td>&lt;12.34</td><td>300</td><td>&lt;12.64</td><td>&lt;12.64</td><td>370</td><td>11.39 ± 0.12</td><td>11.35 ± 0.05</td><td>–</td><td>–</td><td>–</td><td>–</td></tr><tr><td>HD 64972</td><td>280</td><td>&lt;12.38</td><td>&lt;12.38</td><td>280</td><td>&lt;12.68</td><td>&lt;12.68</td><td>340</td><td>11.41 ± 0.10</td><td>11.34 ± 0.04</td><td>–</td><td>–</td><td>–</td><td>–</td></tr><tr><td>HD 60498</td><td>250</td><td>&lt;12.97</td><td>&lt;12.97</td><td>250</td><td>&lt;13.27</td><td>&lt;13.27</td><td>450</td><td>11.50 ± 0.19</td><td>11.49 ± 0.09</td><td>770</td><td>–</td><td>–</td><td>–</td></tr><tr><td>HD 90882</td><td>120</td><td>&lt;12.66</td><td>&lt;12.66</td><td>120</td><td>&lt;12.97</td><td>&lt;12.97</td><td>120</td><td>&lt;11.08</td><td>&lt;11.08</td><td>190</td><td>10.79 ± 0.19</td><td>10.79 ± 0.09</td><td>–</td></tr><tr><td>HD 68761</td><td>290</td><td>13.58 ± 0.04</td><td>13.62 ± 0.07</td><td>290</td><td>13.55 ± 0.06</td><td>13.54 ± 0.11</td><td>320</td><td>11.91 ± 0.08</td><td>11.92 ± 0.06</td><td>410</td><td>12.58 ± 0.03</td><td>12.59 ± 0.01</td><td>–</td></tr><tr><td>HD 74966</td><td>280</td><td>&lt;12.78</td><td>&lt;12.78</td><td>280</td><td>&lt;13.08</td><td>&lt;13.08</td><td>350</td><td>11.07 ± 0.16</td><td>11.10 ± 0.21</td><td>550</td><td>11.89 ± 0.03</td><td>11.81 ± 0.02</td><td>–</td></tr><tr><td>HD 72067</td><td>280</td><td>&lt;13.19</td><td>&lt;13.19</td><td>280</td><td>&lt;13.50</td><td>&lt;13.50</td><td>430</td><td>11.34 ± 0.13</td><td>11.38 ± 0.16</td><td>450</td><td>12.07 ± 0.05</td><td>12.13 ± 0.02</td><td>–</td></tr><tr><td>HD 76341</td><td>220</td><td>13.88 ± 0.02</td><td>13.78 ± 0.02</td><td>220</td><td>13.96 ± 0.02</td><td>13.87 ± 0.06</td><td>220</td><td>11.76 ± 0.09</td><td>11.76 ± 0.07</td><td>330</td><td>12.24 ± 0.04</td><td>12.29 ± 0.01</td><td>21.20 ± 0.08</td></tr><tr><td>HD 76131</td><td>410</td><td>12.63 ± 0.12</td><td>12.51 ± 0.08</td><td>410</td><td>12.79 ± 0.16</td><td>12.87 ± 0.27</td><td>450</td><td>11.75 ± 0.06</td><td>11.75 ± 0.02</td><td>550</td><td>12.38 ± 0.01</td><td>12.37 ± 0.01</td><td>–</td></tr><tr><td>HD 67536</td><td>340</td><td>12.80 ± 0.11</td><td>12.67 ± 0.07</td><td>340</td><td>12.84 ± 0.17</td><td>12.79 ± 0.16</td><td>340</td><td>11.68 ± 0.07</td><td>11.67 ± 0.02</td><td>550</td><td>11.79 ± 0.02</td><td>11.72 ± 0.01</td><td>20.99 ± 0.09</td></tr><tr><td>HD 89587</td><td>290</td><td>12.71 ± 0.08</td><td>12.73 ± 0.15</td><td>290</td><td>12.70 ± 0.12</td><td>12.78 ± 0.29</td><td>270</td><td>–</td><td>–</td><td>470</td><td>–</td><td>–</td><td>–</td></tr><tr><td>HD 88661</td><td>170</td><td>&lt;12.83</td><td>&lt;12.83</td><td>170</td><td>&lt;13.13</td><td>&lt;13.13</td><td>200</td><td>11.58 ± 0.10</td><td>11.58 ± 0.07</td><td>290</td><td>12.02 ± 0.06</td><td>12.03 ± 0.01</td><td>–</td></tr><tr><td>HD 92740</td><td>320</td><td>13.54 ± 0.05</td><td>13.55 ± 0.03</td><td>320</td><td>13.53 ± 0.09</td><td>13.52 ± 0.05</td><td>380</td><td>12.37 ± 0.03</td><td>12.38 ± 0.01</td><td>430</td><td>12.89 ± 0.02</td><td>12.89 ± 0.01</td><td>21.34 ± 0.10</td></tr><tr><td>HD 93131</td><td>290</td><td>13.49 ± 0.06</td><td>13.47 ± 0.06</td><td>290</td><td>13.50 ± 0.10</td><td>13.50 ± 0.11</td><td>370</td><td>12.42 ± 0.03</td><td>12.43 ± 0.01</td><td>450</td><td>12.92 ± 0.01</td><td>12.92 ± 0.01</td><td>21.20 ± 0.10</td></tr><tr><td>HD 94910</td><td>170</td><td>13.97 ± 0.08</td><td>14.09 ± 0.06</td><td>170</td><td>13.80 ± 0.08</td><td>13.83 ± 0.07</td><td>180</td><td>12.50 ± 0.05</td><td>12.50 ± 0.03</td><td>330</td><td>–</td><td>–</td><td>–</td></tr><tr><td>HD 96917</td><td>240</td><td>14.10 ± 0.04</td><td>14.07 ± 0.03</td><td>240</td><td>14.15 ± 0.05</td><td>14.13 ± 0.06</td><td>290</td><td>12.52 ± 0.03</td><td>12.52 ± 0.02</td><td>390</td><td>13.27 ± 0.02</td><td>13.26 ± 0.01</td><td>21.23 ± 0.11</td></tr><tr><td>HD 94963</td><td>250</td><td>13.12 ± 0.04</td><td>13.09 ± 0.19</td><td>250</td><td>13.12 ± 0.06</td><td>13.09 ± 0.33</td><td>320</td><td>12.32 ± 0.04</td><td>12.33 ± 0.03</td><td>430</td><td>12.65 ± 0.02</td><td>12.69 ± 0.01</td><td>–</td></tr></tbody></table>
<table><caption>Table 4 - continued</caption><thead><tr><th rowspan="2">Star</th><th rowspan="2">S/N</th><th colspan="2">Na1 (3302.37)</th><th colspan="2">Na1 (3302.98)</th><th rowspan="2">S/N</th><th rowspan="2">S/N</th><th colspan="2">Tin (3383.76)</th><th rowspan="2">S/N</th><th colspan="2">Ca II (3393.66)</th><th rowspan="2">H1 log<sub>N</sub></th></tr><tr><th>log<sub>N</sub> (Prof)</th><th>log<sub>N</sub> (AOD)</th><th>log<sub>N</sub> (Prof)</th><th>log<sub>N</sub> (AOD)</th><th>log<sub>N</sub> (Prof)</th><th>log<sub>N</sub> (AOD)</th><th>log<sub>N</sub> (Prof)</th><th>log<sub>N</sub> (AOD)</th></tr></thead><tbody><tr><td>HD 97253</td><td>180</td><td>14.00 ± 0.05</td><td>13.97 ± 0.02</td><td>180</td><td>14.05 ± 0.06</td><td>14.07 ± 0.04</td><td>180</td><td>12.45 ± 0.06</td><td>12.51 ± 0.02</td><td>280</td><td>12.99 ± 0.03</td><td>12.97 ± 0.01</td><td>–</td></tr><tr><td>HD 100841</td><td>170</td><td>&lt;12.82</td><td>&lt;12.82</td><td>170</td><td>&lt;13.12</td><td>&lt;13.12</td><td>240</td><td>11.20 ± 0.19</td><td>11.19 ± 0.11</td><td>260</td><td>11.20 ± 0.12</td><td>11.19 ± 0.06</td><td>–</td></tr><tr><td>HD 29138</td><td>260</td><td>12.79 ± 0.21</td><td>12.71 ± 0.50</td><td>260</td><td>12.47 ± 0.25</td><td>12.33 ± 0.45</td><td>300</td><td>12.28 ± 0.06</td><td>12.29 ± 0.02</td><td>450</td><td>12.44 ± 0.02</td><td>12.43 ± 0.01</td><td>20.91 ± 0.10</td></tr><tr><td>HD 105071</td><td>240</td><td>13.41 ± 0.06</td><td>13.43 ± 0.04</td><td>240</td><td>13.50 ± 0.10</td><td>13.56 ± 0.11</td><td>260</td><td>–</td><td>–</td><td>400</td><td>–</td><td>–</td><td>–</td></tr><tr><td>HD 106068</td><td>120</td><td>13.42 ± 0.07</td><td>13.41 ± 0.13</td><td>120</td><td>13.42 ± 0.11</td><td>13.49 ± 0.26</td><td>150</td><td>–</td><td>–</td><td>330</td><td>–</td><td>–</td><td>–</td></tr><tr><td>HD 105056</td><td>250</td><td>13.08 ± 0.11</td><td>13.11 ± 0.14</td><td>250</td><td>13.10 ± 0.18</td><td>13.08 ± 0.24</td><td>230</td><td>12.28 ± 0.06</td><td>12.28 ± 0.03</td><td>260</td><td>12.63 ± 0.02</td><td>12.63 ± 0.01</td><td>21.15 ± 0.10</td></tr><tr><td>HD 109867</td><td>200</td><td>13.43 ± 0.07</td><td>13.41 ± 0.09</td><td>200</td><td>13.46 ± 0.10</td><td>13.44 ± 0.18</td><td>230</td><td>12.23 ± 0.07</td><td>12.22 ± 0.04</td><td>410</td><td>12.68 ± 0.02</td><td>12.68 ± 0.01</td><td>21.11 ± 0.10</td></tr><tr><td>HD 112272</td><td>130</td><td>14.20 ± 0.03</td><td>14.16 ± 0.01</td><td>130</td><td>14.29 ± 0.06</td><td>14.27 ± 0.04</td><td>140</td><td>12.32 ± 0.08</td><td>12.32 ± 0.03</td><td>370</td><td>12.92 ± 0.02</td><td>12.86 ± 0.01</td><td>–</td></tr><tr><td>HD 112842</td><td>250</td><td>13.63 ± 0.06</td><td>13.64 ± 0.04</td><td>250</td><td>13.70 ± 0.09</td><td>13.72 ± 0.08</td><td>280</td><td>12.39 ± 0.05</td><td>12.39 ± 0.02</td><td>–</td><td>–</td><td>–</td><td>–</td></tr><tr><td>HD 113904</td><td>200</td><td>13.01 ± 0.13</td><td>13.07 ± 0.14</td><td>200</td><td>13.10 ± 0.22</td><td>13.15 ± 0.28</td><td>220</td><td>12.31 ± 0.10</td><td>12.30 ± 0.03</td><td>450</td><td>12.79 ± 0.02</td><td>12.79 ± 0.01</td><td>21.15 ± 0.10</td></tr><tr><td>HD 115363</td><td>100</td><td>14.20 ± 0.04</td><td>14.16 ± 0.02</td><td>100</td><td>14.23 ± 0.05</td><td>14.23 ± 0.05</td><td>160</td><td>12.57 ± 0.05</td><td>12.57 ± 0.01</td><td>290</td><td>13.15 ± 0.03</td><td>13.14 ± 0.01</td><td>–</td></tr><tr><td>HD 115842</td><td>190</td><td>14.10 ± 0.04</td><td>14.05 ± 0.01</td><td>190</td><td>14.16 ± 0.05</td><td>14.14 ± 0.03</td><td>200</td><td>12.21 ± 0.07</td><td>12.22 ± 0.03</td><td>300</td><td>12.80 ± 0.02</td><td>12.81 ± 0.01</td><td>21.15 ± 0.12</td></tr><tr><td>HD 136239</td><td>100</td><td>14.18 ± 0.07</td><td>14.20 ± 0.03</td><td>100</td><td>14.21 ± 0.08</td><td>14.19 ± 0.06</td><td>120</td><td>12.68 ± 0.06</td><td>12.69 ± 0.02</td><td>200</td><td>13.22 ± 0.03</td><td>13.19 ± 0.01</td><td>–</td></tr><tr><td>HD 143448</td><td>250</td><td>12.92 ± 0.13</td><td>12.96 ± 0.14</td><td>250</td><td>12.92 ± 0.15</td><td>12.96 ± 0.24</td><td>270</td><td>11.70 ± 0.10</td><td>11.64 ± 0.07</td><td>380</td><td>12.26 ± 0.03</td><td>12.26 ± 0.01</td><td>–</td></tr><tr><td>HD 142758</td><td>270</td><td>13.55 ± 0.05</td><td>13.52 ± 0.05</td><td>270</td><td>13.51 ± 0.06</td><td>13.56 ± 0.10</td><td>270</td><td>12.71 ± 0.06</td><td>12.70 ± 0.01</td><td>350</td><td>12.99 ± 0.02</td><td>12.98 ± 0.01</td><td>–</td></tr><tr><td>HD 137753</td><td>200</td><td>12.43 ± 0.15</td><td>12.38 ± 0.07</td><td>200</td><td>12.53 ± 0.25</td><td>12.51 ± 0.18</td><td>–</td><td>–</td><td>–</td><td>–</td><td>–</td><td>–</td><td>–</td></tr><tr><td>HD 148937</td><td>210</td><td>13.93 ± 0.04</td><td>13.93 ± 0.04</td><td>210</td><td>13.94 ± 0.07</td><td>13.96 ± 0.07</td><td>280</td><td>12.13 ± 0.07</td><td>12.13 ± 0.05</td><td>370</td><td>12.69 ± 0.02</td><td>12.67 ± 0.01</td><td>21.60 ± 0.10</td></tr><tr><td>HD 148379</td><td>150</td><td>13.98 ± 0.05</td><td>13.98 ± 0.02</td><td>150</td><td>13.99 ± 0.07</td><td>14.00 ± 0.05</td><td>180</td><td>12.33 ± 0.05</td><td>12.10 ± 0.04</td><td>250</td><td>12.84 ± 0.02</td><td>12.83 ± 0.01</td><td>–</td></tr><tr><td>HD 148688</td><td>330</td><td>13.85 ± 0.02</td><td>13.81 ± 0.02</td><td>330</td><td>13.88 ± 0.03</td><td>13.90 ± 0.05</td><td>370</td><td>12.18 ± 0.04</td><td>12.20 ± 0.02</td><td>500</td><td>12.86 ± 0.02</td><td>12.83 ± 0.01</td><td>–</td></tr><tr><td>HD 154811</td><td>290</td><td>13.95 ± 0.03</td><td>13.97 ± 0.01</td><td>290</td><td>13.95 ± 0.06</td><td>13.96 ± 0.02</td><td>270</td><td>12.14 ± 0.08</td><td>12.15 ± 0.02</td><td>380</td><td>12.81 ± 0.02</td><td>12.80 ± 0.01</td><td>–</td></tr><tr><td>HD 154873</td><td>310</td><td>13.95 ± 0.03</td><td>13.94 ± 0.02</td><td>310</td><td>14.00 ± 0.04</td><td>14.00 ± 0.04</td><td>310</td><td>12.01 ± 0.06</td><td>12.00 ± 0.04</td><td>410</td><td>12.69 ± 0.02</td><td>12.65 ± 0.01</td><td>–</td></tr><tr><td>HD 156575</td><td>270</td><td>13.76 ± 0.04</td><td>13.74 ± 0.02</td><td>270</td><td>13.76 ± 0.07</td><td>13.76 ± 0.04</td><td>270</td><td>12.12 ± 0.05</td><td>12.12 ± 0.02</td><td>380</td><td>12.63 ± 0.03</td><td>12.62 ± 0.01</td><td>21.26 ± 0.16</td></tr><tr><td>HD 156385</td><td>280</td><td>13.57 ± 0.06</td><td>13.55 ± 0.03</td><td>280</td><td>13.65 ± 0.08</td><td>13.65 ± 0.08</td><td>350</td><td>12.10 ± 0.04</td><td>12.12 ± 0.02</td><td>450</td><td>12.64 ± 0.02</td><td>12.64 ± 0.01</td><td>–</td></tr><tr><td>HD 151932</td><td>210</td><td>14.12 ± 0.03</td><td>14.06 ± 0.02</td><td>210</td><td>14.21 ± 0.03</td><td>14.17 ± 0.05</td><td>310</td><td>12.29 ± 0.06</td><td>12.29 ± 0.03</td><td>550</td><td>12.93 ± 0.01</td><td>12.92 ± 0.01</td><td>21.39 ± 0.11</td></tr><tr><td>HD 152235</td><td>220</td><td>14.14 ± 0.03</td><td>14.10 ± 0.02</td><td>220</td><td>14.18 ± 0.02</td><td>14.18 ± 0.05</td><td>310</td><td>12.26 ± 0.05</td><td>12.27 ± 0.03</td><td>520</td><td>12.92 ± 0.01</td><td>12.89 ± 0.01</td><td>–</td></tr><tr><td>HD 152003</td><td>210</td><td>14.17 ± 0.04</td><td>14.10 ± 0.02</td><td>210</td><td>14.27 ± 0.05</td><td>14.20 ± 0.04</td><td>240</td><td>12.30 ± 0.06</td><td>12.27 ± 0.03</td><td>340</td><td>12.94 ± 0.02</td><td>12.92 ± 0.01</td><td>–</td></tr><tr><td>HD 152270</td><td>240</td><td>13.86 ± 0.04</td><td>13.83 ± 0.02</td><td>240</td><td>13.93 ± 0.05</td><td>13.91 ± 0.05</td><td>250</td><td>12.25 ± 0.07</td><td>12.25 ± 0.03</td><td>450</td><td>12.89 ± 0.01</td><td>12.89 ± 0.01</td><td>–</td></tr><tr><td>HD 145482</td><td>300</td><td>&lt;12.60</td><td>&lt;12.60</td><td>300</td><td>&lt;12.90</td><td>&lt;12.90</td><td>320</td><td>11.21 ± 0.14</td><td>11.16 ± 0.10</td><td>500</td><td>11.06 ± 0.07</td><td>11.08 ± 0.04</td><td>–</td></tr><tr><td>HD 157038</td><td>300</td><td>13.86 ± 0.04</td><td>13.85 ± 0.03</td><td>300</td><td>13.84 ± 0.07</td><td>13.84 ± 0.05</td><td>280</td><td>–</td><td>–</td><td>410</td><td>–</td><td>–</td><td>–</td></tr><tr><td>HD 143275</td><td>280</td><td>13.13 ± 0.05</td><td>13.17 ± 0.06</td><td>280</td><td>13.06 ± 0.06</td><td>13.02 ± 0.08</td><td>330</td><td>11.29 ± 0.15</td><td>11.28 ± 0.07</td><td>–</td><td>–</td><td>–</td><td>21.04 ± 0.08</td></tr><tr><td>HD 163745</td><td>160</td><td>&lt;12.72</td><td>&lt;12.72</td><td>160</td><td>&lt;13.02</td><td>&lt;13.02</td><td>180</td><td>11.81 ± 0.08</td><td>11.77 ± 0.03</td><td>–</td><td>–</td><td>–</td><td>–</td></tr><tr><td>HD 155806</td><td>200</td><td>13.41 ± 0.06</td><td>13.43 ± 0.06</td><td>200</td><td>13.45 ± 0.07</td><td>13.48 ± 0.12</td><td>230</td><td>12.04 ± 0.10</td><td>12.04 ± 0.04</td><td>240</td><td>12.63 ± 0.03</td><td>12.62 ± 0.01</td><td>21.09 ± 0.07</td></tr><tr><td>HD 163758</td><td>230</td><td>13.66 ± 0.04</td><td>13.76 ± 0.06</td><td>230</td><td>13.74 ± 0.06</td><td>13.72 ± 0.11</td><td>250</td><td>12.56 ± 0.05</td><td>12.56 ± 0.02</td><td>550</td><td>13.09 ± 0.02</td><td>13.08 ± 0.01</td><td>21.23 ± 0.18</td></tr><tr><td>HD 148184</td><td>270</td><td>13.70 ± 0.02</td><td>13.66 ± 0.01</td><td>270</td><td>13.86 ± 0.02</td><td>13.81 ± 0.03</td><td>300</td><td>11.62 ± 0.08</td><td>11.67 ± 0.03</td><td>450</td><td>12.02 ± 0.02</td><td>12.01 ± 0.01</td><td>21.15 ± 0.09</td></tr></tbody></table>
<figure><img src="image_11.png" /><figcaption>**Figure 4.** The logarithm of the total column density derived from the component fitting (listed in Table 3) compared to the logarithm of the total column density calculated using the AOD method. The solid and dashed lines represent the best-fitting line and the 1σ standard deviation in the points, respectively. The rms scatter and Pearson correlation coefficients are 0.059, 0.993; 0.055, 0.994; 0.044, 0.997 and 0.027, 0.997 for panels (a)–(d), respectively.</figcaption></figure>

<figure><img src="image_12.png" /><figcaption>**Figure 5.** Comparison of the logarithm of the total column density from each line of the Na I UV doublet. The solid and dashed lines represent the best-fitting line and the 1σ standard deviation in the points, respectively. The rms scatter and Pearson correlation coefficient are 0.078 and 0.988, respectively.</figcaption></figure>

<table><caption>**Table 5.** Comparisons with previous work.</caption><thead><tr><th rowspan="2">Star</th><th rowspan="2">Species</th><th colspan="2">Total column density</th><th rowspan="2">Reference</th></tr><tr><th>This paper</th><th>Other work</th></tr></thead><tbody><tr><td>HD 164794</td><td>Na I</td><td>13.59</td><td>13.58</td><td>1</td></tr><tr><td>HD 164794</td><td>Ti II</td><td>12.08</td><td>11.84</td><td>1</td></tr><tr><td>HD 164794</td><td>Ca II</td><td>12.62</td><td>12.63</td><td>1</td></tr><tr><td>HD 36862</td><td>Na I</td><td>13.20</td><td>&gt;12.89</td><td>4</td></tr><tr><td>HD 36862</td><td>Ti II</td><td>11.74</td><td>11.73</td><td>2</td></tr><tr><td>HD 36862</td><td>Ca II</td><td>12.50</td><td>12.52</td><td>4</td></tr><tr><td>HD 50896</td><td>Ti II</td><td>12.05</td><td>12.18</td><td>3</td></tr><tr><td>HD 50896</td><td>Ca II</td><td>12.47</td><td>12.45</td><td>3</td></tr><tr><td>HD 143275</td><td>Na I</td><td>13.10</td><td>&gt;12.79</td><td>4</td></tr><tr><td>HD 143275</td><td>Ti II</td><td>11.29</td><td>11.02</td><td>2</td></tr></tbody></table>

(1) Welsh et al. (1997), (2) Stokes (1978), (3) Hobbs (1984) and (4) Hobbs (1974).

totals have been calculated as the sum of the individual components, tabulated in Table 3, along each sightline. We also present the S/N measured in the vicinity of each of the lines, along with the total H I column density towards each line of sight. The H I data have been taken from the *IUE* observations of Diplas & Savage (1994) for all sightlines, except for HD 50896, HD 52918 and HD 148184, where the results are from Fruscione et al. (1994), and HD 58978 from Savage, Edgar & Diplas (1990).
<figure><img src="image_13.png" /><figcaption>**Figure 6.** Plots of the logarithm of the total column density of (panel a) NaI, (panel b) Ti II and (panel c) Ca II against the logarithm of the distance to the star (in pc). Open circles represent upper limits to the column density. The solid and dashed lines represent the best-fitting line and the 1σ standard deviation in the points, respectively. The error in the distance is 25 per cent (approximately 0.12 dex in the logarithm). The rms scatter and Pearson correlation coefficients are 0.501, 0.399; 0.287, 0.776 and 0.330, 0.817 for panels (a)–(c), respectively.</figcaption></figure>

## 4.3 Correlations in total column densities

In this section, we discuss correlations in the derived column densities against parameters such as distance, reddening and H I column density. Where best fits are performed, all slopes assume all free parameters.

### 4.3.1 Correlations with distance

In Fig. 6, we plot the logarithm of the total column density derived from profile fitting for each species against the logarithm of the stellar distance (in pc), along with an unweighted linear best fit to the data points. Fig. 6(a) shows a weak correlation between the Na column density and distance, although with the wide scatter of points and small correlation coefficient this correlation may not be significant. However, in Fig. 6(b), we see a strong correlation between the Ti column density and the distance, and a similar strong correlation for Ca in Fig. 6(c), both being in agreement with that reported by W97. This supports other studies which find that Ti and Ca have a fairly even spatial distribution, although we should note that there are a number of points in which the column density of Ti can vary by as much as one order of magnitude for stars at similar distances. W97 find this same spread in the column density and conclude that this is expected due to the non-uniform distribution of interstellar gas in the spiral arms. In the W97 survey, the majority of the stellar targets lie within 1 kpc. However, most of the targets in our sample lie out to 3.5 kpc. Smoker et al. (2003) observed a greater depletion of Ca II K along sightlines with distances of less than ~500 pc and they associate this with the Local Bubble, an elliptical, hot, low-density region of the ISM which has significant X-ray emissivity out to ~100 pc and is likely to have been formed via a supernova event, see for example, Frisch (1998) and Frisch & York (1983). We do not see this effect in Fig. 6(c) but given the limited number of our sightlines which lie within the Local Bubble, this is unlikely to be significant. Finally, we find that the correlations of Ti and Ca with distance are very similar and this is further evidence that Ti and Ca are mostly associated with the same interstellar regions.

### 4.3.2 Correlations with distance above the Galactic plane

We also examine the correlation between the total column density of each species and the perpendicular height, *z*, of the stellar target from the Galactic plane. Following similar methods to W97, we plot the projected column density, $N_{\text{tot}} \times \sin b$ against $|z|$, along with the unweighted linear best fittings to the data points, for Na, Ti and Ca in Figs 7(a)–(c), respectively. Again we find a weaker correlation in the Na plot, but good correlations for both Ti and Ca, with the best-fitting lines having very similar correlation coefficients of 0.880 and 0.864, respectively. We note that distance uncertainties contribute an error of ~0.12 dex, compared with the rms scatter of 0.29 and 0.33 dex for Ti and Ca, hence the Ti and Ca relationships are remarkably tight. Also, although we sample similar Galactic heights to W97, we find a much tighter distribution of the points about the best-fitting line for Ti and Ca. Hence, we similarly conclude that the column density of each species increases with height above the Galactic plane, and this trend is in agreement with other sources such as Edgar & Savage (1989). Although our sample does not include lines of sight with sufficiently high *z* to calculate the Galactic scale height of Ti II or Ca II, our results are in agreement with the limits reported. Edgar & Savage (1989) also report the smooth distribution of Ti II and Ca II, in agreement with our results and they find that these species are generally associated with the smooth distribution of the intercloud medium.

### 4.3.3 Correlations with reddening

In Fig. 8, we plot the correlation between the logarithm of the total column density per pc and the reddening per kpc along the line of sight for each of the three species under investigation. Note that HD 148184 has been excluded from the plot as it appears to have an anomalously high value of redening per kpc (4.26 kpc⁻¹).

As expected, we find evidence of increasing column density along sightlines with higher reddenings, as reported by Stokes (1978) and
<figure><img src="image_14.png" /><figcaption>**Figure 7.** Plots of the logarithm of the total column density of (panel a) Na I, (panel b) Ti II and (panel c) Ca II against the perpendicular distance to the star, z, (in pc). Open circles represent upper limits to the column density. The solid and dashed lines represent the best-fitting line and the 1σ standard deviation in the points, respectively. The error in the distance is 25 per cent (approximately 0.12 dex in the logarithm). The rms scatter and Pearson correlation coefficients are 0.424, 0.564; 0.272, 0.880 and 0.321, 0.864 for panels (a)–(c), respectively.</figcaption></figure>

<figure><img src="image_15.png" /><figcaption>**Figure 8.** Plots of the logarithm of the total column density of (panel a) Na I, (panel b) Ti II and (panel c) Ca II per pc against reddening per kpc. Open circles represent upper limits to the column density. The uncertainty in the reddening per kpc is approximately 25 per cent. The solid and dashed lines represent the best-fitting line and the 1σ standard deviation in the points, respectively. The rms scatter and Pearson correlation coefficients are 0.381, 0.597; 0.251, 0.534 and 0.284, 0.486 for panels (a)–(c), respectively.</figcaption></figure>

W97. At very low values of reddening, we generally do not observe the Na I UV doublet along as many sightlines as we observe Ti or Ca. Hence, we see more upper limits at low reddenings per kpc in Fig. 8(a) compared to Figs 8(b) and (c). The correlation of the total Na column density with reddening appears to be stronger than that of Ti and Ca. The correlation coefficient in Fig. 8(a) is 0.597, compared to Figs 8(b) and (c) where the correlation coefficients are 0.534 and 0.486 respectively. Although the scatter of points in Fig. 8(a) is greater than that in Figs 8(b) and (c), this

stronger correlation appears to be significant. This effect is also seen in W97.

### 4.3.4 Correlations with total neutral hydrogen column density along the sightlines

In Figs 9(a)–(c), we plot the correlation between the logarithm of the total column density per pc and the total neutral hydrogen column density per pc derived from Lyα absorption for each species, taken
<figure><img src="image_16.png" /><figcaption>**Figure 9.** Plots of the logarithm of the total column density of (panel a) Na I, (panel b) Ti II and (panel c) Ca II per pc against the logarithm of the total H I column density per pc along the line of sight. Open circles represent upper limits to the column density. The solid and dashed lines represent the best-fitting line and the 1σ standard deviation in the points, respectively. The uncertainty in the H I column density per pc is typically 0.10 dex. The rms scatter and Pearson correlation coefficients are 0.427, 0.539; 0.227, 0.459 and 0.293, 0.477 for panels (a)–(c), respectively.</figcaption></figure>

from Diplas & Savage (1994), Fruscione et al. (1994) and Savage et al. (1990). Given the limited number of sightlines for which we have hydrogen column densities and that we sample a range of only 1.5 mag in hydrogen column density per pc, it is difficult to derive accurate correlations. From Fig. 9, it appears that there are similar correlations comparing the column density of both Ti and Ca with the hydrogen column density. The best-fitting line in Fig. 9(a) gives a stronger correlation between the total Na column density per pc and the total neutral hydrogen column density along the sightline, although given the larger scatter in Fig. 9(a) this may not be significant. The similarity of Figs 9(b) to (c) may indicate that Ti II and Ca II occur in the same regions of the ISM. Indeed, we see very similar depletion patterns between Ti II and Ca II and this is fully discussed in Section 4.3.6 We note that Wakker & Mathis (2000) also find similar scatters in the plots of Ca and Ti column density with H I column density (a 1σ standard deviation of 0.4 in the log for each species). This disagrees with the findings of W97, who report a much higher degree of scatter in the Ca plot compared to Ti, and reasonably conclude that Ca II absorption is more affected by ionization and depletion than is Ti II. We note that W97 samples a much larger range in N(H I) than do our observations. Our data have values in the rms scatter of 0.29 for Ca II and 0.23 for Ti II. A priori, the scatter would be expected to be larger in Ca II than in Ti II, as the former is not the primary ionization stage in the warm ISM (WIM), although the observed difference is small and may be a statistical variation.

Ferlet, Vidal-Madjar & Gry (1985) discuss the use of Na I as a tracer of H I in the diffuse ISM via the relationship:

$$ \log N(\text{NaI}) = 1.04 \times \log N(\text{H}_1 + \text{H}_2) - (-9.09) $$

as derived from Na I D lines. These authors also report that at low reddening $[E(B - V) < 0.3]$, this relation is independent of reddening. In Fig. 10, we plot the total Na column density against the value for H I at low reddening, $E(B - V) < 0.3$, and also show an unweighted best-fitting line to the data points. We note that at these

<figure><img src="image_17.png" /><figcaption>**Figure 10.** Correlation between the logarithm of the total Na I column density derived from a profile fit of the Na I UV doublet at 3302 Å and the logarithm of the total H I column density at low reddening, $E(B - V) < 0.3$. The solid line represents the best fit to our data points, given as points with error bars. The triangles represent the Na I column density derived from the weaker line of the Na I D doublet at 5893 Å. The open circles represent the Na I D column density corrected for saturation, using the corrections from Savage & Sembach (1991). The dashed line represents the best-fitting line to these corrected points. The discrepant point at a H I column density of 20.53 dex has not been included in the best-fitting lines.</figcaption></figure>

reddenings, we do not believe the contribution of H$_2$ to be significant compared to that of H I. We have also calculated Na column densities from the weaker line of the Na I D doublet at 5893 Å for these sightlines where possible, the results being plotted as triangles. We find excellent agreement between these results and those predicted by the Ferlet et al. (1985) relation. From the best-fitting line to the points plotted as triangles in Fig. 10 (note, this best-fitting line is
not shown in the figure), we calculate the relationship between Na I and H I to be

$$ \log N(\text{NaI}) = 1.07 \times \log N(\text{HI}) - 9.66 $$

This contrasts with the relationship:

$$ \log N(\text{NaI}) = 1.76 \times \log N(\text{HI}) - 23.91 $$

derived from the best-fitting line to the Na I UV points shown as the solid line in Fig. 10, although given the scatter and low number of data points the significance of this relation is uncertain. A lack of H I column densities derived in a consistent manner percludes us from deriving a more robust relation.

In W97, it is reported that the ultraviolet (UV) Na I UV doublet can underestimate the true Na I column density by up to 20 per cent. We believe this to be due to the fact that higher velocity clouds which appear in the Na I D lines and are significantly offset from the strongest feature do not appear in the UV Na I transitions due to the inherent weakness of these lines. On the other hand, the high strength of the Na I D lines means that saturation effects cause an underestimate of the column density for the strongest feature of these lines. This effect can be much more important than the underestimation from the UV lines, which goes some way to explaining the offset between our UV sodium column density and the column density from the Na I D lines. Savage & Sembach (1991) estimate the correction that one needs to apply to account for saturation, based on the difference between the column density derived from each line of the doublet. We have applied these corrections to the Na I D column density and these are plotted as open circles in Fig. 10. A best-fitting line to these points gives a relationship of

$$ \log N(\text{NaI}) = 1.23 \times \log N(\text{HI}) - 13.01 $$

Although this correction reduces the discrepancy between the column densities from the Na I UV and D lines, there is still a significant offset between them. This offset approximately corresponds to an underestimate of 30 per cent in the column density derived from the Na I D lines compared to using the Na I UV transitions.

<figure><img src="image_18.png" /><figcaption>**Figure 12.** Correlations between the logarithm of the column density of associated components of Ti II and Ca II. The solid and dashed lines represent the best-fitting line and the 1σ standard deviation in the points about this line. The rms scatter and Pearson correlation coefficient are 0.319 and 0.786, respectively. Open circles represent upper limits to the column density of an individual component.</figcaption></figure>

### 4.3.5 Correlations between the column density of each species

In Figs 11(a)–(c), we present plots of the correlations between the column densities derived from each species, and we see good correlation in all three plots. We calculate abundance ratios between the three species to be 0.04 ± 0.01, 0.30 ± 0.04 and 0.13 ± 0.02 for N(Ti II)/N(Na I), N(Ti II)/N(Ca II) and N(Ca II)/N(Na I), respectively, where the quoted uncertainty is the 1σ standard deviation divided by the square root of the number of points used to determine the ratio. In Fig. 11(b), we see a particularly strong correlation between the Ti II and the Ca II abundance and our N(Ti II)/N(Ca II) ratio agrees well with the value of 0.29 ± 0.03 determined by W97.

In Fig. 12, we plot the column density of individual Ti II components against that of the associated Ca II component listed in Table 3.

<figure><img src="image_19.png" /><figcaption>**Figure 11.** Correlations between the logarithm of the total column densities derived from each species. The open circles represent upper limits to column densities. The solid and dashed lines represent the best-fitting line and the 1σ standard deviation in the points, respectively. The rms scatter and Pearson correlation coefficients are 0.275, 0.573; 0.178, 0.920, and 0.385, 0.643 for panels (a)–(c), respectively.</figcaption></figure>
We have not plotted cases where we see two resolved features in one species and only one feature at a similar velocity in the other species. Similarly, if there are overlapping components of either Ti II or Ca II that lie within the FWHM of either the main or the overlapping component, these components are excluded from the plot. The same rejection criteria were applied with respect to the upper limits. The $N(\text{Ti II})/N(\text{Ca II})$ ratio based on the components is 0.26 which is in excellent agreement with that derived from the totals. It should be noted that in the derivation of this ratio we have not included those points plotted as open circles. We note that the rms scatter and correlation coefficient are larger and smaller, respectively, than when comparing the total column density along a line of sight (0.32 dex compared to 0.18 dex for the rms scatter and 0.78 compared to 0.92 for the Pearson correlation coefficient). This may be due to the fact that the components are associated if they lie within 3 km s$^{-1}$ in velocity space, and could in fact be separate parcels of gas.

Finally, we note that for low upper limit values of Ca II, the points appear to be mainly associated with higher upper limits for Ti II. This may simply be an effect of the higher upper limits for Ti compared to Ca upper limits being due to the weakness of the Ti line compared to the Ca line. For the very low total column densities of Ca, we see a similar effect in Fig. 11(b) although given that this is in only four points on the plots its significance is in doubt. This is in contrast to W97 (fig. 8a) where the opposite effect is seen, low column densities of Ca II seem to correspond to lower than expected upper limits to the Ti column density. Given that this is only seen in the upper limits and not for any real detections, this may be an effect of the methodology which was used to estimate the upper limits. In fig. 8(c) of W97, where they plot Ti against Ca for individual components, this effect is not seen.

### 4.3.6 Depletions in the column density along each line of sight

In Fig. 13, we plot the depletion of the species with respect to the perpendicular height and the reddening along the line of sight, in a similar method to that used by W97. The depletion is calculated as the ratio of the abundance of the element to the Solar system value. Solar system abundances of 6.37, 5.00, and 6.41 for Na, Ti and Ca, respectively, are obtained from Lodders (2003), where the abundance of the element is taken as its total column density relative to the H I column density along the line of sight. Previous work (e.g. Gondhalekar 1985; Crinklaw et al. 1994) indicates that the depletion of both Ti and Ca increase in line with increasing column density. Both elements show the same slope with increasing column density, indicating that these elements only trace the warm intercloud medium. In this paper, we hence restrict ourselves to correlations in depletion of the three species studied with distance above the Galactic plane and reddening in line with W97.

Fig. 13(a) shows a weak correlation between the height, $|z|$, and the depletion for Na I, in the sense of a higher depletion at high $z$, but given the scatter in the plot (Pearson correlation coefficient of -0.25), this does not appear significant. In Figs 13(b) and (c), we see evidence for lower depletions of Ti and Ca at higher values of $|z|$, consistent with less dust with increasing distance from the Galactic plane. In Fig. 13(d), we see a correlation between the depletion of Na and the reddening along the line of sight, with again less depletion at higher reddenings. Given the small scatter and large correlation coefficient, the correlation appears to be significant. In contrast, we find evidence of constant depletions of Ti and Ca at all reddenings, shown in Figs 13(e) and (f). This disagrees with the

<figure><img src="image_20.png" /><figcaption>**Figure 13.** Panels (a)–(c) show the depletion as a function of the perpendicular distance to the star to the Galactic plane for Na I, Ti II and Ca II, respectively. Panels (d)–(f) show the depletion as a function of the reddening along the sightline to the star for Na I, Ti II and Ca II, respectively. The dotted line represents the average depletion derived from our sample. Open circles represent lower limits to the depletion. The solid and dashed lines represent the best-fitting line and the $1\sigma$ standard deviation in the points, respectively. The rms scatter and Pearson correlation coefficients are 0.322, -0.253; 0.236, 0.592; 0.285, 0.370; 0.239, 0.695; 0.291, -0.101 and 0.306, -0.046 for panels (a)–(f), respectively.</figcaption></figure>
work of de Boer et al. (1986) who find that the depletion of all metals increases with increasing $E(B-V)$, although for Ti II there were only eight data points. However, our finding of a lack of correlation agrees with W97 who find little evidence in Ti II for such an effect with $E(B-V) > 0.2$. We note that the scatter and range in values of depletion found in this paper for Ti II of -1.4 to -2.8 dex are somewhat smaller than found by W97 whose depletion values range from -0.5 to -2.7 dex.

Considering the decreasing Na depletion with increasing $E(B - V)$, we associate the sightlines with higher reddenings as having a significant amount of $H_2$. We have been able to obtain the $H_2$ column density for one line of sight, HD 148184, at high reddening [$E(B - V) = 0.53$] from Fruscione et al. (1994), and we find that this is 30 per cent of the H I column density. For an element that is primarily in clouds, the exclusion of $H_2$ will cause the total observed H column density to be decreased, causing an observed increase in the abundance of the element and a corresponding decrease in depletion which is what we observe in Fig. 13(d) at high values of reddening. On the other hand, regions with higher $E(B - V)$ values are associated with dust on to which elements are removed from the gas phase, which causes an increased depletion. Hence the two affects act in different directions. We note that, for example, Phillips, Pettini & Gondhalekar (1984) find that over a range of column densities, the depletion of sodium is essentially constant.

### 4.3.7 $N(Ti	ext{II})/N(Ca	ext{II})$ ratio

In order to reliably conclude that Ti II and Ca II do indeed occur in similar environments, we plot the $N(Ti	ext{II})/N(Ca	ext{II})$ ratio against distance to the stellar target, total H I column density along sightline and reddening in Figs 14(a)–(c), respectively. We also plot the average $N(Ti	ext{II})/N(Ca	ext{II})$ ratio as a dotted line in these figures. Fig. 14(a) shows a number of ‘discrepant’ points, that is, with higher than average $N(Ti	ext{II})/N(Ca	ext{II})$ ratios. These sightlines have in common that, given errors in their distance estimates, they can be associated within the Local Bubble. The only peculiarities in these sightlines are that for Ca II K in HD 100841, the lines are broad and weak and for HD 145482 the lines are also relatively weak. From each

of these plots we conclude that, in general, $N(Ti	ext{II})/N(Ca	ext{II})$ ratio is constant over distance, cloud density and reddening, and hence we can infer that Ti II and Ca II normally occur in the same regions. The rms of the scatter when we plot the total column density of Ti II against Ca II is some 0.18 dex. The mode in the errors in the total column densities for each species are 0.02 dex for Ca II and 0.05 dex for Ti II, so the intrinsic scatter on the data is only some 30–40 per cent. We recall that the observed depletion is dependent in each sightline on the fraction of warm and cold gas present in each component (Spitzer 1985), the dust content (ions being removed from the gas phase by sticking on to grains) and the ionizing radiation field. The fact that Ca II does not vary much with respect to Ti II was initially surprising, as it suggests that the amount of Ca II (not the dominant ionization stage) does not change much with the radiation field. However, at least when comparing the WIM to low-density H II regions, the work of Sembach et al. (2000) predicts that the relative fraction in these transitions remains constant. For example, in their composite model of the WIM by Sembach et al. (2000), the ionization fraction is 0.21 for Ca II, 0.79 for Ca III, 0.59 for Ti II and 0.41 for Ti III. For WIM regions with the fraction of neutral hydrogen $x_{\text{edge}}$, is greater than 0.1, the corresponding values of the ionization fraction for their model is 0.19 for Ca II, 0.79 for Ca III, 0.45 for Ti II and 0.52 for Ti III. Finally, for the $x_{\text{edge}} = 0.1$ model for a low-density H II region, the ionization fractions are 0.06 for Ca II, 0.94 for Ca III, 0.18 for Ti II and 0.63 for Ti III. In these models at least, the relative Ti II/Ca II ionization fractions are thus a factor of 3 different in both cases. Hence if the models are accurate and the sightline is comprised only of WIM and H II regions, the strong correlation between Ti II and Ca II is not unexpected. Of course, the above discussion does not take into account the presence of dark clouds in which both the elements are heavily depleted.

## 4.4 Components

### 4.4.1 Intermediate- and high-velocity components

In order to classify the interstellar components, we have observed them as low-, intermediate- or high-velocity components (LVCs,

<figure><img src="image_21.png" /><figcaption>**Figure 14.** Panels (a)–(c) plot the $N(Ti	ext{II})/N(Ca	ext{II})$ ratio as a function of distance to the target, total H I column density and reddening, respectively. The dotted lines represent the average $N(Ti	ext{II})/N(Ca	ext{II})$ ratio.</figcaption></figure>
<table><caption>**Table 6.** List of sightlines showing intermediate- and high-velocity features in absorption.</caption><thead><tr><th rowspan="2">Star</th><th rowspan="2">l<br>(°)</th><th rowspan="2">b<br>(°)</th><th rowspan="2">d<br>(pc)</th><th rowspan="2">Component<br>number</th><th colspan="2">Na I (3302)</th><th colspan="2">Ti II (3384)</th><th colspan="2">Ca II (3934)</th><th rowspan="2">Type</th></tr><tr><th>v<sub>LSR</sub></th><th>v<sub>Dev</sub></th><th>v<sub>LSR</sub></th><th>v<sub>Dev</sub></th><th>v<sub>LSR</sub></th><th>v<sub>Dev</sub></th></tr></thead><tbody><tr><td>HD 164794</td><td>6.01</td><td>-1.21</td><td>1585</td><td>2</td><td>-</td><td>-</td><td>-31.2</td><td>-31.2</td><td>-</td><td>-</td><td>IVC</td></tr><tr><td>HD 167264</td><td>10.46</td><td>-1.74</td><td>2109</td><td>5</td><td>-</td><td>-</td><td>43.7</td><td>30.9</td><td>-</td><td>-</td><td>IVC</td></tr><tr><td>HD 171432</td><td>14.62</td><td>-4.98</td><td>4014</td><td>1</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-65.2</td><td>-65.2</td><td>IVC</td></tr><tr><td>HD 171432</td><td>14.62</td><td>-4.98</td><td>4014</td><td>2</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-62.5</td><td>-62.5</td><td>IVC</td></tr><tr><td>HD 171432</td><td>14.62</td><td>-4.98</td><td>4014</td><td>3</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-47.2</td><td>-47.2</td><td>IVC</td></tr><tr><td>HD 171432</td><td>14.62</td><td>-4.98</td><td>4014</td><td>12</td><td>-</td><td>-</td><td>-</td><td>-</td><td>92.6</td><td>48.7</td><td>IVC</td></tr><tr><td>HD 171432</td><td>14.62</td><td>-4.98</td><td>4014</td><td>13</td><td>-</td><td>-</td><td>-</td><td>-</td><td>117.4</td><td>73.5</td><td>IVC</td></tr><tr><td>HD 169454</td><td>17.54</td><td>-0.67</td><td>1359</td><td>1</td><td>-</td><td>-</td><td>-40.2</td><td>-40.2</td><td>-</td><td>-</td><td>IVC</td></tr><tr><td>HD 37490</td><td>200.73</td><td>-14.03</td><td>304</td><td>1</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-45.7</td><td>-45.7</td><td>IVC</td></tr><tr><td>HD 50896</td><td>234.76</td><td>-10.08</td><td>1393</td><td>1</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-65.0</td><td>-65.0</td><td>IVC</td></tr><tr><td>HD 60498</td><td>247.20</td><td>-6.64</td><td>936</td><td>1</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-41.2</td><td>-41.2</td><td>IVC</td></tr><tr><td>HD 60498</td><td>247.20</td><td>-6.64</td><td>936</td><td>2</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-31.2</td><td>-31.2</td><td>IVC</td></tr><tr><td>HD 60498</td><td>247.20</td><td>-6.64</td><td>936</td><td>12</td><td>-</td><td>-</td><td>-</td><td>-</td><td>53.4</td><td>44.3</td><td>IVC</td></tr><tr><td>HD 68761</td><td>254.37</td><td>-1.62</td><td>1473</td><td>1</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-55.3</td><td>-55.3</td><td>IVC</td></tr><tr><td>HD 68761</td><td>254.37</td><td>-1.62</td><td>1473</td><td>2</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-39.2</td><td>-39.2</td><td>IVC</td></tr><tr><td>HD 68761</td><td>254.37</td><td>-1.62</td><td>1473</td><td>10</td><td>-</td><td>-</td><td>-</td><td>-</td><td>50.8</td><td>38.8</td><td>IVC</td></tr><tr><td>HD 74966</td><td>258.08</td><td>3.93</td><td>658</td><td>7</td><td>-</td><td>-</td><td>-</td><td>-</td><td>35.7</td><td>31.8</td><td>IVC</td></tr><tr><td>HD 74966</td><td>258.08</td><td>3.93</td><td>658</td><td>8</td><td>-</td><td>-</td><td>-</td><td>-</td><td>50.5</td><td>46.6</td><td>IVC</td></tr><tr><td>HD 72067</td><td>262.08</td><td>-3.08</td><td>488</td><td>1</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-105.8</td><td>-105.8</td><td>HVC</td></tr><tr><td>HD 89587</td><td>279.83</td><td>5.19</td><td>900</td><td>1</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-40.1</td><td>-37.4</td><td>IVC</td></tr><tr><td>HD 93131</td><td>287.67</td><td>-1.08</td><td>2600</td><td>1</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-67.4</td><td>-57.1</td><td>IVC</td></tr><tr><td>HD 93131</td><td>287.67</td><td>-1.08</td><td>2600</td><td>2</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-51.4</td><td>-41.0</td><td>IVC</td></tr><tr><td>HD 94910</td><td>289.18</td><td>-0.69</td><td>6000</td><td>1</td><td>-117.3</td><td>-105.1</td><td>-</td><td>-</td><td>-</td><td>-</td><td>HVC</td></tr><tr><td>HD 94910</td><td>289.18</td><td>-0.69</td><td>6000</td><td>2</td><td>-79.4</td><td>-67.2</td><td>-</td><td>-</td><td>-</td><td>-</td><td>IVC</td></tr><tr><td>HD 94910</td><td>289.18</td><td>-0.69</td><td>6000</td><td>3</td><td>-64.5</td><td>-52.3</td><td>-66.2</td><td>-54.0</td><td>-</td><td>-</td><td>IVC</td></tr><tr><td>HD 96917</td><td>289.28</td><td>3.06</td><td>2910</td><td>1</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-70.8</td><td>-58.5</td><td>IVC</td></tr><tr><td>HD 96917</td><td>289.28</td><td>3.06</td><td>2910</td><td>11</td><td>-</td><td>-</td><td>-</td><td>-</td><td>60.1</td><td>60.1</td><td>IVC</td></tr><tr><td>HD 94963</td><td>289.76</td><td>-1.81</td><td>3257</td><td>1</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-89.0</td><td>-76.1</td><td>IVC</td></tr><tr><td>HD 94963</td><td>289.76</td><td>-1.81</td><td>3257</td><td>2</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-54.0</td><td>-41.0</td><td>IVC</td></tr><tr><td>HD 94963</td><td>289.76</td><td>-1.81</td><td>3257</td><td>3</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-44.8</td><td>-31.9</td><td>IVC</td></tr><tr><td>HD 97253</td><td>290.79</td><td>0.09</td><td>2415</td><td>1</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-47.4</td><td>-33.7</td><td>IVC</td></tr><tr><td>HD 29138</td><td>297.99</td><td>-30.54</td><td>3530</td><td>1</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-77.6</td><td>-56.9</td><td>IVC</td></tr><tr><td>HD 106068</td><td>298.51</td><td>-0.41</td><td>2824</td><td>1</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-85.0</td><td>-61.3</td><td>IVC</td></tr><tr><td>HD 106068</td><td>298.51</td><td>-0.41</td><td>2824</td><td>2</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-75.6</td><td>-51.9</td><td>IVC</td></tr><tr><td>HD 109867</td><td>301.71</td><td>-4.35</td><td>3264</td><td>1</td><td>-</td><td>-</td><td>-63.0</td><td>-33.3</td><td>-63.1</td><td>-33.4</td><td>IVC</td></tr><tr><td>HD 136239</td><td>321.23</td><td>-1.75</td><td>2350</td><td>1</td><td>-</td><td>-</td><td>-65.2</td><td>-31.6</td><td>-64.2</td><td>-30.6</td><td>IVC</td></tr><tr><td>HD 148937</td><td>336.37</td><td>-0.22</td><td>1380</td><td>1</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-102.4</td><td>-87.3</td><td>IVC</td></tr><tr><td>HD 148688</td><td>340.72</td><td>4.35</td><td>1452</td><td>1</td><td>-</td><td>-</td><td>-41.7</td><td>-28.0</td><td>-46.1</td><td>-32.4</td><td>IVC</td></tr><tr><td>HD 148688</td><td>340.72</td><td>4.35</td><td>1452</td><td>8</td><td>-</td><td>-</td><td>-</td><td>-</td><td>34.1</td><td>34.1</td><td>IVC</td></tr><tr><td>HD 151932</td><td>343.22</td><td>1.43</td><td>1413</td><td>1</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-56.2</td><td>-44.4</td><td>IVC</td></tr><tr><td>HD 151932</td><td>343.22</td><td>1.43</td><td>1413</td><td>2</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-44.0</td><td>-32.2</td><td>IVC</td></tr><tr><td>HD 151932</td><td>343.22</td><td>1.43</td><td>1413</td><td>11</td><td>-</td><td>-</td><td>-</td><td>-</td><td>51.5</td><td>51.5</td><td>IVC</td></tr><tr><td>HD 152235</td><td>343.31</td><td>1.10</td><td>1861</td><td>1</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-75.3</td><td>-58.8</td><td>IVC</td></tr><tr><td>HD 152235</td><td>343.31</td><td>1.10</td><td>1861</td><td>13</td><td>-</td><td>-</td><td>-</td><td>-</td><td>39.8</td><td>39.8</td><td>IVC</td></tr><tr><td>HD 152003</td><td>343.33</td><td>1.41</td><td>2687</td><td>1</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-62.9</td><td>-36.3</td><td>IVC</td></tr><tr><td>HD 152270</td><td>343.49</td><td>1.16</td><td>1900</td><td>10</td><td>-</td><td>-</td><td>-</td><td>-</td><td>31.7</td><td>31.7</td><td>IVC</td></tr><tr><td>HD 157038</td><td>349.95</td><td>-0.79</td><td>1444</td><td>1</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-87.3</td><td>-79.6</td><td>IVC</td></tr><tr><td>HD 157038</td><td>349.95</td><td>-0.79</td><td>1444</td><td>2</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-69.6</td><td>-61.9</td><td>IVC</td></tr><tr><td>HD 157038</td><td>349.95</td><td>-0.79</td><td>1444</td><td>3</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-59.1</td><td>-51.4</td><td>IVC</td></tr><tr><td>HD 157038</td><td>349.95</td><td>-0.79</td><td>1444</td><td>4</td><td>-</td><td>-</td><td>-47.8</td><td>-40.1</td><td>-48.9</td><td>-41.2</td><td>IVC</td></tr><tr><td>HD 155806</td><td>352.59</td><td>2.87</td><td>1064</td><td>1</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-37.0</td><td>-33.0</td><td>IVC</td></tr><tr><td>HD 163758</td><td>355.36</td><td>-6.10</td><td>4103</td><td>1</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-46.9</td><td>-30.8</td><td>IVC</td></tr><tr><td>HD 163758</td><td>355.36</td><td>-6.10</td><td>4103</td><td>10</td><td>-</td><td>-</td><td>-</td><td>-</td><td>38.9</td><td>38.9</td><td>IVC</td></tr><tr><td>HD 163758</td><td>355.36</td><td>-6.10</td><td>4103</td><td>11</td><td>-</td><td>-</td><td>-</td><td>-</td><td>90.4</td><td>90.4</td><td>HVC</td></tr></tbody></table>

IVCs and HVCs, respectively), we have calculated the expected velocity range in which one would expect to see interstellar clouds based on the direction of the sightline and the distance to the stellar target. To calculate the velocity range, we use the methodology of Wakker (1991), in that we assume a flat rotation curve with $v_{rot} = 220$ km s$^{-1}$ at $r > 0.5$ kpc, decreasing linearly towards the Galactic Centre, together with equations from Mihalas & Binney (1981).

A deviation velocity for interstellar cloud components which lie outside the expected velocity range is calculated, where the deviation velocity is defined as the difference between the velocity of the component and the nearest limit of the expected velocity range (Wakker 1991). We classify LVCs as having absolute values of their deviation velocities below 30 km s$^{-1}$, IVCs between 30 and 90 km s$^{-1}$, and HVCs greater than 90 km s$^{-1}$. In Table 6, we tabulate all
the IVCs and HVCs detected along our sightlines. As this paper is not primarily concerned with IVCs and HVCs, and we also do not have access to H<sub>I</sub> emission spectra at present, we are hence unable to confirm that our detected IVCs and HVCs are real interstellar clouds. We must emphasize that given the nearby nature of many of the stars, it is unlikely that they are true HVCs/IVCs but this possibility should not be discounted. Although high-velocity clouds are thought to reside either in the Galactic halo or possibly at extragalactic distances (e.g. Wakker & van Woerden 1997; Braun & Burton 1999), they can also arise from shocks created in the ISM by supernova blast waves. In this paper, we will restrict ourselves to a brief discussion of several of the more interesting sightlines, although a full study of both IVCs and HVCs will be carried out in a future paper.

### 4.4.2 HD 171432

We see five IVCs in the Ca II K line and these have also been identified in the Ca II H feature and hence these lines are unlikely to be stellar transitions of another species. We have correlated our sightline with data from the H I survey of high-velocity interstellar clouds in the Southern hemisphere (Morras et al. 2000), and we do not find any nearby H I clouds at similar velocities to our HVCs, although we have not inspected the actual H I data.

HD 171432 lies along the line of sight to the Scutum Supershell and Callaway et al. (2000) report a kinematically derived distance to the Supershell of 3.3 kpc with a diameter of ~290 pc. Our spectroscopic distance estimate puts the star at a distance of 4.0 kpc and so the IVCs appear to be associated with this feature. We also see some evidence for IVCs in the Ti II spectra although these have not been fitted. On closer inspection of the spectra, we see evidence of many small-strength features which do not appear to be noise. Based on the FWHM of the stellar lines of the star, these features are clearly not stellar in nature (unless there is a binary companion present), but they may be evidence of small-scale structure in the Scutum Supershell.

### 4.4.3 HD 72067

We see a single strong HVC along this sightline which also appears in Ca II H. This sightline lies along the same sightline as the Vela supernova remnant which Cha, Sembach & Danks (1999) report to lie at a distance of 250 pc. Our distance estimate of 488 pc would place HD 72067 within and possibly beyond the Vela supernova remnant and as many previously observed HVCs have been seen along sightlines which pass through this remnant, for example, as reported by Slavin, Nichols & Blair (2004), our observation of an HVC is not unexpected.

### 4.4.4 HD 94910

This is the only sightline in which we detect an HVC in the Na I UV data, and also appears in the Ca II K line. Note that we have not fitted the interstellar components of the Ca II K line due to the difficulty of accurately fitting a baseline to the continuum. The SIMBAD database classifies HD 94910 as a Wolf-Rayet star and the high-velocity feature we see may be associated with the star rather than the ISM, as Wolf-Rayet stars are known to have many peculiar features (Leitherer & Chavarria 1987), such as stellar-wind bubbles this could explain our high-velocity features. Indeed, we find that over two-thirds of our stellar targets which are classified as Wolf-Rayet's show IVCs or HVCs.

### 4.4.5 HD 163758

Again we have confirmed the existence of the high-velocity feature in the Ca II H line, although similarly to HD 94910 this star is classified as a Wolf-Rayet star and as such the HVC may be a circumstellar feature. A search of the Morras et al. (2000) H I data base does not find any nearby HVCs at a similar velocity to our detected feature.

## 5 CONCLUSIONS

We have obtained spectra towards 74 early-type stellar targets from the UVES POP survey, at a velocity resolution of 3.75 km s⁻¹. We have studied the interstellar Na I UV doublet at 3302 Å, Ti II at 3383 Å and Ca II at 3933 Å. The average S/N per pixel for the spectra are 260, 300 and 430, respectively, which far exceeds that in previous work in a sample of this size. Column densities were measured for each component along each line of sight, with the individual components being summed to obtain the total. This quantity was also calculated by the AOD method, which is in excellent agreement with the total generated by the fitting of each individual component. There is also good agreement between the total column densities derived from each line of the Na I UV doublet. The median of the errors in individual components are 0.06, 0.06 and 0.02 dex for Na, Ti and Ca components, respectively. In general, we have not studied cases where the stellar line is of a similar width and velocity to the interstellar profile, and so we have avoided stellar contamination of our derived column densities.

## 5.1 General correlations

We have investigated the dependence of the total column density of each species along the line of sight to a star with distance, reddening and total H I column density. Our stars span distances from 52 to 6000 pc, with the maximum height from the Galactic plane, |z|, being 1793 pc. We find a strong positive correlation between Ti and Ca column densities and distance, and a similar correlation for Na although with much more scatter. We also find a good correlation between the column densities and |z|, although again the correlation is weaker in Na. Our sightlines have values of reddening E(B - V) of up to 1.0, and some correlation between the column density per pc of each species and the reddening per kpc has been found. We find similar correlations between the H I column density per pc and the column density per pc of Ca and Ti. There is evidence of a stronger correlation between Na and H I but given the scatter of the points this may not be significant. Wakker & Mathis (2000) have previously found this large dispersion, and have thus cautioned against for example using non-detections of Na to set limits on the distances of high-velocity clouds. The observed scatter in Na and H I is attributed by these authors to the fact that it is not the dominant ionization stage in the ISM, so ionization effects may play a more important role. This certainly calls into question the accuracy of using the Na column density as an indicator of the value for H I. We also find that the column density derived from the Na I D lines, generally used to predict the H I values, appears to underestimate the column density relative to the UV lines that we have studied. Even when the saturation corrections of Savage & Sembach (1991) are applied to the column density derived from the Na I D lines it still appears to underestimate the Na column density. For Na column densities greater than 13 dex, the corrected values underestimate the column density by as much as 0.3 dex relative to column density derived from the UV lines.
**5.2 Depletions**

The depletion of each species relative to the Solar system value has been correlated with $|z|$ and $E(B-V)$. We find some evidence for decreasing depletion with increasing $z$ for both Ti and Ca, with no correlation with depletion and reddening for these species. For Na, we find decreasing depletion with increasing $E(B-V)$, some of which may be caused by the conversion of $H_i$ to $H_2$.

**5.3 N(Ti II)/N(Ca II) ratio**

We find a good correlation between the Ti II and Ca II column densities, both in the total values and those from individual components that are observed in both species. The ratio from the total is 0.30 compared to that from the individual components of 0.26. Our ratios compare very well with the value of $0.29 \pm 0.03$ calculated by W97. The similarity between our plots of the correlation of Ti and Ca with each of the different parameters reinforces the possibility that the species show good correspondence if the Ca ionization balance is controlled by the average interstellar radiation field, and the relative Ca and Ti depletions are relatively constant in the clouds (Welty et al. 1996; Wakker & Mathis 2000).

**5.4 Future work**

As discussed in Section 4.4.1, many of our sightlines show strong IVC and HVC features. A future paper will involve a more detailed analysis of these components, using the Villa-Elissa H I survey and the current observations to provide improved distance limits to IVCs and HVCs.

**ACKNOWLEDGMENTS**

We would like to thank the staff of the Very Large Telescope, Paranal for the work involved in producing the POP survey. ESO DDT programme ID 266.D-5655, http://www.eso.org/uvespop. IH and JVS gratefully acknowledge the ESO Director Generals Discretionary fund which provided financial support for IH for this work. FPK is grateful to AWE Aldermaston for the award of a William Penney Fellowship. This research has made use of the SIMBAD database, operated at CDS, Strasbourg, France. We would also like to thank the referee who provided many useful comments and suggestions to the initial draft of the paper.

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This paper has been typeset from a *TEX/LATEX* file prepared by the author.