1 00:00:00,010 --> 00:00:05,010 - [Brittany] Okay, so today, I'm Brittany, 2 00:00:06,410 --> 00:00:09,400 I just ended my fourth year of graduate school. 3 00:00:09,400 --> 00:00:11,700 And today I'm gonna talk about M-band observations 4 00:00:11,700 --> 00:00:13,720 of the coldest brown dwarfs. 5 00:00:13,720 --> 00:00:17,663 we use M-band spectroscopy to detect CO in these objects. 6 00:00:22,590 --> 00:00:27,590 Okay, so I'm at ExoPAG talking about brown dwarfs, 7 00:00:28,040 --> 00:00:29,860 but the reason I study brown dwarfs 8 00:00:29,860 --> 00:00:32,020 is to primarily understand 9 00:00:32,020 --> 00:00:33,820 what directly imaged gas giant planets 10 00:00:33,820 --> 00:00:35,660 will look like in the future. 11 00:00:35,660 --> 00:00:38,090 So brown dwarfs and planets, 12 00:00:38,090 --> 00:00:39,680 we think form in different ways, 13 00:00:39,680 --> 00:00:42,690 but ultimately they're both objects that are gas balls 14 00:00:42,690 --> 00:00:44,300 that have molecules in their atmosphere 15 00:00:44,300 --> 00:00:45,780 that create opacity sources 16 00:00:45,780 --> 00:00:47,480 that we can detect in our spectra. 17 00:00:48,660 --> 00:00:50,810 So on the left here, 18 00:00:50,810 --> 00:00:54,250 I have a figure, it's a color magnitude diagram 19 00:00:54,250 --> 00:00:57,750 and on the Y-axis, absolute magnitude 20 00:00:57,750 --> 00:01:00,100 is a proxy for effective temperature. 21 00:01:00,100 --> 00:01:01,690 And so we have warmer objects on the top, 22 00:01:01,690 --> 00:01:03,140 cooler objects on the bottom. 23 00:01:04,240 --> 00:01:06,740 And these orange-brownish points, 24 00:01:06,740 --> 00:01:11,020 those are the data points for brown dwarfs, 25 00:01:11,020 --> 00:01:13,710 and they go through the L, T, and Y sequence here. 26 00:01:13,710 --> 00:01:15,670 And then these blue points are the data 27 00:01:15,670 --> 00:01:18,180 for directly imaged exoplanets. 28 00:01:18,180 --> 00:01:21,880 Now, as you'll notice, directly imaged exoplanets 29 00:01:21,880 --> 00:01:24,420 follow the sequence along with brown dwarfs. 30 00:01:24,420 --> 00:01:26,460 There are some differences, but what you'll notice 31 00:01:26,460 --> 00:01:28,880 is that for every directly imaged exoplanet, 32 00:01:28,880 --> 00:01:30,840 there is a brown dwarf with similar temperature 33 00:01:30,840 --> 00:01:33,080 that you can study and maybe figure out 34 00:01:33,080 --> 00:01:34,460 what these directly imaged planets 35 00:01:34,460 --> 00:01:36,580 should look like when you get to follow up 36 00:01:36,580 --> 00:01:38,480 with better instruments in the future. 37 00:01:40,020 --> 00:01:42,623 I'm focused on Y-dwarfs down here. 38 00:01:43,760 --> 00:01:46,090 These are the coldest brown dwarfs we know about now. 39 00:01:46,090 --> 00:01:48,800 And as you'll notice there are no directly imaged planets 40 00:01:48,800 --> 00:01:50,490 in this region right now. 41 00:01:50,490 --> 00:01:52,700 So the project I'm talking about 42 00:01:52,700 --> 00:01:56,070 is specifically related to spectroscopy of Y-dwarfs 43 00:01:56,070 --> 00:01:58,400 which will tell us about the directly imaged planets 44 00:01:58,400 --> 00:02:01,357 we will be able to see with things like HabEx or LUVOIR. 45 00:02:04,970 --> 00:02:09,650 Okay, so things we wanna know by studying brown dwarfs, 46 00:02:09,650 --> 00:02:11,300 you know, what gases or clouds 47 00:02:11,300 --> 00:02:13,610 we can expect to see in future planets, 48 00:02:13,610 --> 00:02:14,443 or we just wanna know 49 00:02:14,443 --> 00:02:17,210 what temperature things like water clouds. 50 00:02:17,210 --> 00:02:19,800 When should we expect these features to show up 51 00:02:19,800 --> 00:02:21,540 in other planets. 52 00:02:21,540 --> 00:02:23,280 And lastly, regarding instruments, 53 00:02:23,280 --> 00:02:25,020 what wavelengths coverage and resolutions 54 00:02:25,020 --> 00:02:27,720 are needed to make the best out of future instruments? 55 00:02:31,290 --> 00:02:33,540 So this slide is to show you spectroscopically 56 00:02:33,540 --> 00:02:36,010 why brown dwarfs and directly imaged exoplanets 57 00:02:36,010 --> 00:02:37,550 are very similar. 58 00:02:37,550 --> 00:02:41,520 Here, I have a normalized spectrum of 51 Eri. 59 00:02:41,520 --> 00:02:44,210 This wavelength covers the J, H, and K bands 60 00:02:44,210 --> 00:02:46,560 from one to two microns 61 00:02:46,560 --> 00:02:49,160 and the black data points here with these error bars, 62 00:02:49,160 --> 00:02:51,360 those are the spectra from 51 Eri b, 63 00:02:51,360 --> 00:02:53,380 it's one of the coldest directly imaged exoplanets 64 00:02:53,380 --> 00:02:55,350 we know about today. 65 00:02:55,350 --> 00:02:58,670 And this red line here, 66 00:02:58,670 --> 00:03:03,360 that is a spectrum of a T-dwarf of similar temperature. 67 00:03:03,360 --> 00:03:04,734 And as you can see, 68 00:03:04,734 --> 00:03:07,800 the data for both of these objects line up, 69 00:03:07,800 --> 00:03:10,260 there are some discrepancies, you know, here, 70 00:03:10,260 --> 00:03:13,290 but ultimately you could see that both this planet 71 00:03:13,290 --> 00:03:15,540 and this brown dwarf share the same absorption features 72 00:03:15,540 --> 00:03:16,470 due to methane. 73 00:03:16,470 --> 00:03:18,270 And so you could have looked at this brown dwarf 74 00:03:18,270 --> 00:03:19,570 and figured out, you know, 75 00:03:19,570 --> 00:03:21,350 what's the right resolution I needed 76 00:03:21,350 --> 00:03:23,853 to actually see this methane in 51 Eri b. 77 00:03:27,930 --> 00:03:29,910 So a lot of the characterization studies 78 00:03:29,910 --> 00:03:31,830 for directly imaged exoplanets and brown dwarfs 79 00:03:31,830 --> 00:03:34,370 are typically done in the near-infrared, 80 00:03:34,370 --> 00:03:37,760 but we need to extend this wavelength color coverage 81 00:03:37,760 --> 00:03:39,510 out to the mid-infrared when we're talking 82 00:03:39,510 --> 00:03:41,720 about characterizing colder gas giant planets 83 00:03:41,720 --> 00:03:42,753 and Y-dwarfs. 84 00:03:43,960 --> 00:03:46,610 So on this figure on the left, 85 00:03:46,610 --> 00:03:50,030 we have like the band pass flux 86 00:03:50,030 --> 00:03:51,467 over a specific wavelength range 87 00:03:51,467 --> 00:03:56,310 divided by the full flux from each model plotted 88 00:03:56,310 --> 00:03:59,190 on the X axis, how to give an effective temperature. 89 00:03:59,190 --> 00:04:02,220 So a very high temperature from one to two microns 90 00:04:02,220 --> 00:04:06,290 that band pass, and captures most of the flux 91 00:04:06,290 --> 00:04:08,410 from these brown dwarfs and exoplanets. 92 00:04:08,410 --> 00:04:11,640 But as you go to cooler and cooler temperatures, 93 00:04:11,640 --> 00:04:14,550 most of the flux is emitted from three to five microns. 94 00:04:14,550 --> 00:04:19,550 And below under about 500 Kelvin, methane sweeps out 95 00:04:19,630 --> 00:04:21,910 of a lot of the flux between three to four microns. 96 00:04:21,910 --> 00:04:23,640 So most of this flux beyond here 97 00:04:23,640 --> 00:04:25,690 is actually between four to five microns. 98 00:04:28,060 --> 00:04:30,140 So the line here is 51 Eri, 99 00:04:30,140 --> 00:04:32,380 kind of the coldest plant we know about now. 100 00:04:32,380 --> 00:04:34,500 And if we wanna look towards the future, 101 00:04:34,500 --> 00:04:35,920 we need to be trying to characterize 102 00:04:35,920 --> 00:04:40,920 and detect these objects in the three to five micron range. 103 00:04:43,200 --> 00:04:46,350 So to summarize, some of the best contrast we can get 104 00:04:46,350 --> 00:04:48,600 for these cool exoplanets that are, 105 00:04:48,600 --> 00:04:49,580 I understand there are some people 106 00:04:49,580 --> 00:04:50,420 who do reflected light, 107 00:04:50,420 --> 00:04:53,130 but I'm talking about very widely separated gas giants. 108 00:04:53,130 --> 00:04:54,610 Some of the best contrasts you can achieve 109 00:04:54,610 --> 00:04:56,940 is between three to five microns. 110 00:04:56,940 --> 00:04:57,773 In addition to this, 111 00:04:57,773 --> 00:05:00,320 there are numerous potential opacity sources 112 00:05:00,320 --> 00:05:02,410 that can be detected and constrained 113 00:05:02,410 --> 00:05:05,140 like phosphene, carbon monoxide, carbon dioxide, 114 00:05:05,140 --> 00:05:07,170 which you have to do from space, methane, 115 00:05:07,170 --> 00:05:09,290 ammonia, and et cetera. 116 00:05:09,290 --> 00:05:10,960 And future instruments 117 00:05:10,960 --> 00:05:12,740 need to utilize this wavelength region. 118 00:05:12,740 --> 00:05:14,750 One of those proposed instruments is SCALES 119 00:05:14,750 --> 00:05:15,850 which will go on KECK. 120 00:05:24,670 --> 00:05:28,430 So there have been previous studies done 121 00:05:28,430 --> 00:05:33,080 on the M-band regarding the coldest brown dwarf WISE 0855, 122 00:05:34,080 --> 00:05:36,750 and WISE 0855 is 250 Kelvin, 123 00:05:36,750 --> 00:05:39,470 and it's only about 125 Kelvin hotter 124 00:05:39,470 --> 00:05:42,423 than our own planet Jupiter in our solar system. 125 00:05:43,330 --> 00:05:47,330 And so, here again I have a normalized spectra plotted. 126 00:05:47,330 --> 00:05:50,180 This is from 4.4 microns to 5.2 microns, 127 00:05:50,180 --> 00:05:51,453 this crosses the M-band. 128 00:05:52,670 --> 00:05:55,190 And the plot, the black data points with the error bars, 129 00:05:55,190 --> 00:05:57,990 that's the M-band spectra of WISE 0855, 130 00:05:57,990 --> 00:05:59,537 that's taken with Gemini (indistinct). 131 00:06:00,393 --> 00:06:03,520 And the spectrum of Jupiter is this blue line here 132 00:06:05,110 --> 00:06:06,560 as you can see in the figure. 133 00:06:07,730 --> 00:06:10,720 The dominant absorption feature you see 134 00:06:10,720 --> 00:06:13,623 in the WISE 0855 spectrum is due to water here. 135 00:06:14,950 --> 00:06:18,380 And the difference between WISE 0855 and Jupiter 136 00:06:18,380 --> 00:06:21,290 is that Jupiter mostly has its water absorption feature 137 00:06:21,290 --> 00:06:24,100 on the red side, whereas on the blue side, 138 00:06:24,100 --> 00:06:27,160 you have this deep feature due to phosphene. 139 00:06:27,160 --> 00:06:28,940 Now, the only reason Jupiter has phosphene 140 00:06:28,940 --> 00:06:31,740 is because it's being brought up by convection 141 00:06:31,740 --> 00:06:33,970 from the deeper, hotter layers in this planet. 142 00:06:33,970 --> 00:06:35,880 So even though WISE 0855 and Jupiter 143 00:06:35,880 --> 00:06:37,070 are fairly close in temperature, 144 00:06:37,070 --> 00:06:38,710 they have very different mixing properties 145 00:06:38,710 --> 00:06:41,090 that ultimately affects how the spectra look 146 00:06:41,090 --> 00:06:42,083 when we take data. 147 00:06:46,420 --> 00:06:50,110 So my project that was accepted, it was recently accepted. 148 00:06:50,110 --> 00:06:53,180 I have to just finish the proofs, but it's on the archive. 149 00:06:53,180 --> 00:06:55,645 The goal of this project is to extend our studies 150 00:06:55,645 --> 00:06:58,373 of these very cool objects, 151 00:06:59,650 --> 00:07:02,910 basically across from 750 Kelvin down to Jupiter. 152 00:07:02,910 --> 00:07:04,700 We don't wanna just check two objects 153 00:07:04,700 --> 00:07:05,533 and say, "Oh, they're different." 154 00:07:05,533 --> 00:07:08,040 We wanna understand is there a trend 155 00:07:08,040 --> 00:07:11,310 across the lower effective temperature range? 156 00:07:11,310 --> 00:07:13,003 So for this paper, 157 00:07:14,910 --> 00:07:19,620 we have these sample of objects here, Jupiter and WISE 0855 158 00:07:19,620 --> 00:07:22,230 had their data published previously. 159 00:07:22,230 --> 00:07:25,190 and Gliese 570 D and 2MASS 0415 160 00:07:25,190 --> 00:07:27,410 have already had their data published 161 00:07:27,410 --> 00:07:30,720 and they were taken with Gemini and the AKARI spacecraft. 162 00:07:30,720 --> 00:07:33,020 I took data for these four objects, 163 00:07:33,020 --> 00:07:35,540 WISE 0313 which is a T-dwarf, 164 00:07:35,540 --> 00:07:38,890 UGPS 0722 which is also a late T-dwarf, 165 00:07:38,890 --> 00:07:42,850 And then WISE 2056 and WISE 1541, which are Y-dwarfs. 166 00:07:42,850 --> 00:07:44,400 Now this is only four objects, 167 00:07:44,400 --> 00:07:46,830 but this is like 50 hours of Gemini data right here, 168 00:07:46,830 --> 00:07:50,143 which took a lot to get done and to reduce. 169 00:07:51,000 --> 00:07:53,720 These objects are ordered by their effective temperature 170 00:07:53,720 --> 00:07:57,860 determined by photometric fits to cloudless models. 171 00:07:57,860 --> 00:07:59,910 So that's how I'm ordering them, Jupiter, 172 00:08:00,860 --> 00:08:03,623 that temperature is the published one from Cassini. 173 00:08:07,090 --> 00:08:08,620 So while doing this project, 174 00:08:08,620 --> 00:08:13,420 what we expected to see is across 600 to 200 Kelvin, 175 00:08:13,420 --> 00:08:16,670 we expected only water to effect these spectra. 176 00:08:16,670 --> 00:08:20,190 So, and figure out how to normalize M-band spectra 177 00:08:20,190 --> 00:08:23,300 and the black, yellow, and blue lines 178 00:08:23,300 --> 00:08:25,350 represent different models at 600 Kelvin, 179 00:08:25,350 --> 00:08:27,540 400 Kelvin, and 200 Kelvin. 180 00:08:27,540 --> 00:08:28,830 And so the only difference, 181 00:08:28,830 --> 00:08:30,020 they all show water absorption, 182 00:08:30,020 --> 00:08:32,000 but the only difference that should change 183 00:08:32,000 --> 00:08:35,130 if everything was equilibrium is the slope of the objects. 184 00:08:35,130 --> 00:08:36,087 So the 200 Kelvin object 185 00:08:36,087 --> 00:08:38,773 has a slightly steeper slope than the 600 Kelvin one. 186 00:08:41,450 --> 00:08:42,940 But what we actually saw 187 00:08:42,940 --> 00:08:45,960 was a variety of spectral slopes 188 00:08:45,960 --> 00:08:48,653 across this very small effective temperature range. 189 00:08:49,670 --> 00:08:50,950 So again, 190 00:08:50,950 --> 00:08:53,900 I just have a large panel of normalized M-band spectra 191 00:08:53,900 --> 00:08:56,260 on the top, we have Gliese 570 D, 192 00:08:56,260 --> 00:08:58,053 it has this peak feature here, 193 00:08:59,128 --> 00:09:02,753 2MASS 0415, it looks a little bit flat here. 194 00:09:02,753 --> 00:09:06,647 And then, 0313, there's maybe a slight peak here. 195 00:09:06,647 --> 00:09:08,923 And then it looks a little bit flat here. 196 00:09:08,923 --> 00:09:13,923 UGPS 0722, this one, it has the most like distinct spectrum 197 00:09:14,070 --> 00:09:17,690 where you have this dip here and a peak here 198 00:09:17,690 --> 00:09:20,640 and it sweeps out and it gets brighter out on the red side. 199 00:09:20,640 --> 00:09:23,123 This feature is due to carbon monoxide. 200 00:09:23,970 --> 00:09:25,890 And then WISE 2056 basically 201 00:09:25,890 --> 00:09:30,260 just gets brighter at redder wavelengths. 202 00:09:30,260 --> 00:09:33,200 WISE 1641 is essentially flat. 203 00:09:33,200 --> 00:09:35,710 And then we have WISE 0855 204 00:09:35,710 --> 00:09:37,580 where it still looks like, 205 00:09:37,580 --> 00:09:41,270 I re-reduced the data for this paper as a sanity check, 206 00:09:41,270 --> 00:09:44,350 but there's still water dominating the spectrum 207 00:09:44,350 --> 00:09:45,183 for this object. 208 00:09:45,183 --> 00:09:47,690 And then Jupiter with water and phosphene absorption. 209 00:09:52,130 --> 00:09:54,700 So ultimately the first thing we learned 210 00:09:54,700 --> 00:09:58,460 was that water can't explain these spectra alone. 211 00:09:58,460 --> 00:10:01,960 So in each panel I have the data of each brown dwarf. 212 00:10:01,960 --> 00:10:03,750 Those are the colors data points, 213 00:10:03,750 --> 00:10:07,730 and the light gray points are the equilibrium model 214 00:10:07,730 --> 00:10:09,170 plotted at the same effective temperature 215 00:10:09,170 --> 00:10:11,120 of that brown dwarf. 216 00:10:11,120 --> 00:10:13,530 So in the case of like Gliese 570 D 217 00:10:13,530 --> 00:10:16,140 and almost every single brown dwarf there, 218 00:10:16,140 --> 00:10:19,570 the model has excess flux on the blue side of the spectrum. 219 00:10:19,570 --> 00:10:23,270 It's a little bit here too, and you can see it here. 220 00:10:23,270 --> 00:10:26,300 And then for UGPS 0722, 221 00:10:26,300 --> 00:10:28,440 it basically crisscrosses with the data 222 00:10:28,440 --> 00:10:30,740 and it's a very poor fit. 223 00:10:30,740 --> 00:10:35,740 And then for WISE 2056 and 1541 we have the same issue. 224 00:10:36,100 --> 00:10:38,470 And it's even a bad fit for WISE 0855, 225 00:10:38,470 --> 00:10:42,270 even though in Andy's paper, it was shown that water 226 00:10:42,270 --> 00:10:44,423 was initially a good fit for the spectrum. 227 00:10:45,970 --> 00:10:47,670 So the next thing we did 228 00:10:47,670 --> 00:10:51,203 was actually take the same cloudless models, 229 00:10:52,040 --> 00:10:55,330 and actually added CO to see if we could get a better fit. 230 00:10:55,330 --> 00:10:57,270 Because we wanna understand, you know, 231 00:10:57,270 --> 00:10:58,830 what's the one knob we can turn 232 00:10:58,830 --> 00:11:00,563 to best fit most of these spectra. 233 00:11:03,300 --> 00:11:05,330 And so that's what does it. 234 00:11:05,330 --> 00:11:09,470 So again, I had the same data plotted as color data points, 235 00:11:09,470 --> 00:11:10,740 and then the light gray points 236 00:11:10,740 --> 00:11:12,740 are the same effective temperature model 237 00:11:12,740 --> 00:11:16,960 just with the amount of CO in the atmosphere turned up. 238 00:11:16,960 --> 00:11:20,020 So for again, Gliese 570 D we get a pretty good fit 239 00:11:20,020 --> 00:11:23,240 by adding the CO to have a mole fraction 240 00:11:23,240 --> 00:11:25,270 of 10 to the negative four. 241 00:11:25,270 --> 00:11:27,540 And then the same, we have a better fit 242 00:11:27,540 --> 00:11:32,540 for 2MASS 0415, 0313, UGPS 0722, and so on and so forth. 243 00:11:35,060 --> 00:11:36,700 - [Mike] Brittany, we're at 12 minutes. 244 00:11:36,700 --> 00:11:37,860 - [Brittany] Thanks, Mike. 245 00:11:37,860 --> 00:11:42,270 And so these CO fractions here, they're way higher 246 00:11:42,270 --> 00:11:45,260 than what you would expect to see at equilibrium. 247 00:11:45,260 --> 00:11:48,810 So, and typically these brown dwarfs are very cold. 248 00:11:48,810 --> 00:11:51,520 That means that the dominant carbon-bearing molecule 249 00:11:51,520 --> 00:11:54,230 should be methane, not CO. 250 00:11:54,230 --> 00:11:55,090 So what that means 251 00:11:55,090 --> 00:11:57,230 is that there's disequilibrium chemistry going on 252 00:11:57,230 --> 00:11:58,080 in these objects. 253 00:11:59,854 --> 00:12:02,604 (faint speaking) 254 00:12:05,290 --> 00:12:07,630 So this is a 2D schematic 255 00:12:07,630 --> 00:12:09,110 of what a brown dwarf looks like. 256 00:12:09,110 --> 00:12:10,700 If everything was in an equilibrium, 257 00:12:10,700 --> 00:12:11,990 you would have the top of the atmosphere 258 00:12:11,990 --> 00:12:14,200 where most of the gas should be methane, 259 00:12:14,200 --> 00:12:16,340 and deep down, once you go to the center of the object, 260 00:12:16,340 --> 00:12:18,353 it should be carbon monoxide dominated. 261 00:12:20,060 --> 00:12:23,420 This gray line represents where our data reaches down to, 262 00:12:23,420 --> 00:12:24,990 so if you took a spectrum in this case, 263 00:12:24,990 --> 00:12:28,400 you would only detect methane and see nothing in the M-band. 264 00:12:28,400 --> 00:12:29,790 But we know brown dwarfs... 265 00:12:31,610 --> 00:12:34,250 Interesting, okay, well there's supposed to be CO here, 266 00:12:34,250 --> 00:12:37,320 but brown dwarfs are convective, 267 00:12:37,320 --> 00:12:39,480 and that means that you may have CO gas 268 00:12:39,480 --> 00:12:41,450 being brought up to the upper layers 269 00:12:41,450 --> 00:12:43,490 where your data is sensitive. 270 00:12:43,490 --> 00:12:48,490 But there's some timescale that CO turns into methane, 271 00:12:49,150 --> 00:12:52,340 but if this mixing is way faster than that timescale, 272 00:12:52,340 --> 00:12:54,430 you'll have a layer that's a little bit methane 273 00:12:54,430 --> 00:12:55,490 and a little bit of CO. 274 00:12:55,490 --> 00:12:57,740 And so that's what we detect in our spectrum. 275 00:13:00,430 --> 00:13:01,850 So this convective mixing, 276 00:13:01,850 --> 00:13:03,650 or just any type of mixing in general 277 00:13:03,650 --> 00:13:06,970 is characterized by Kzz. 278 00:13:06,970 --> 00:13:11,970 And so Kzz is determined by the length scale squared 279 00:13:12,070 --> 00:13:14,020 divided by the timescale of mixing, 280 00:13:14,020 --> 00:13:16,520 and the units are centimeter squared over seconds. 281 00:13:18,290 --> 00:13:21,220 And so just briefly, this is for the theorist, 282 00:13:21,220 --> 00:13:23,550 but feel free to email me later. 283 00:13:23,550 --> 00:13:25,660 How do we actually estimate this value? 284 00:13:25,660 --> 00:13:27,560 We find where the measured CO abundance 285 00:13:27,560 --> 00:13:30,200 occurs along a pressure-temperature profile 286 00:13:30,200 --> 00:13:32,420 to calculate the chemical timescale 287 00:13:32,420 --> 00:13:34,070 at that pressure and temperature. 288 00:13:35,800 --> 00:13:37,330 We set this chemical timescale 289 00:13:37,330 --> 00:13:38,710 equal to the mixing timescale, 290 00:13:38,710 --> 00:13:41,070 that's when something's quenched. 291 00:13:41,070 --> 00:13:42,820 And three, we calculate the length scale 292 00:13:42,820 --> 00:13:45,310 at a specific pressure and temperature. 293 00:13:45,310 --> 00:13:46,160 And this length scale 294 00:13:46,160 --> 00:13:49,130 is dependent on temperature and surface gravity. 295 00:13:49,130 --> 00:13:50,150 And we repeat this 296 00:13:50,150 --> 00:13:51,840 for different pressure-temperature profiles 297 00:13:51,840 --> 00:13:53,690 at different surface gravities. 298 00:13:53,690 --> 00:13:55,840 Typically brown dwarfs, especially with cold ones, 299 00:13:55,840 --> 00:13:57,960 there are no surface gravity indicators. 300 00:13:57,960 --> 00:13:59,750 So you typically have to pick a age range 301 00:13:59,750 --> 00:14:01,673 and get a surface gravity range. 302 00:14:03,580 --> 00:14:05,360 So what we find with this project 303 00:14:05,360 --> 00:14:10,360 is that cooler atmospheres overall have stronger mixing. 304 00:14:10,400 --> 00:14:11,233 In this plot, 305 00:14:11,233 --> 00:14:14,420 I have Kzz plotted against effective temperature. 306 00:14:14,420 --> 00:14:16,350 Jupiter is plotted as the hexagon here. 307 00:14:16,350 --> 00:14:17,370 It has one data point 308 00:14:17,370 --> 00:14:19,820 'cause we know what the mass of Jupiter is. 309 00:14:19,820 --> 00:14:20,970 The rest of the brown dwarfs, 310 00:14:20,970 --> 00:14:22,440 we have a couple data points 311 00:14:23,590 --> 00:14:25,913 representative of different surface gravities 312 00:14:26,950 --> 00:14:28,990 which we calculate Kzz with. 313 00:14:28,990 --> 00:14:33,100 And so Jupiter and WISE 0855 are a little bit up here, 314 00:14:33,100 --> 00:14:34,350 and as you get warmer, 315 00:14:34,350 --> 00:14:38,300 there's noticeably a smaller strength of mixing here. 316 00:14:38,300 --> 00:14:41,310 In addition to this, we have these theoretical curves, 317 00:14:41,310 --> 00:14:44,930 what Kzz or the strength of mixing should be 318 00:14:44,930 --> 00:14:46,760 assuming that all of the heat of the object 319 00:14:46,760 --> 00:14:49,210 contributes to the convective mixing. 320 00:14:49,210 --> 00:14:51,910 So in the case of Jupiter and WISE 0855, 321 00:14:51,910 --> 00:14:53,610 they're mixing at close 322 00:14:53,610 --> 00:14:56,230 or at their theoretical upper limits, 323 00:14:56,230 --> 00:14:58,950 whereas these warmer objects 324 00:14:58,950 --> 00:15:01,493 are mixing well below that limit. 325 00:15:04,320 --> 00:15:08,123 So ultimately, we wanna know why that is. 326 00:15:09,470 --> 00:15:11,410 First point, models predict brown dwarfs 327 00:15:11,410 --> 00:15:14,823 and gas giants colder than 400 Kelvin at around here. 328 00:15:18,030 --> 00:15:21,040 Yeah, models predict that brown dwarfs and gas giant planets 329 00:15:21,040 --> 00:15:24,620 that are cooler than 400 Kelvin are fully convective. 330 00:15:24,620 --> 00:15:26,300 Whereas these warmer objects here 331 00:15:26,300 --> 00:15:29,530 may have radiative zones in between these convective layers. 332 00:15:29,530 --> 00:15:31,310 And so by having those there, 333 00:15:31,310 --> 00:15:33,520 conviction may be a little more sluggish 334 00:15:33,520 --> 00:15:35,560 and may inhibit the amount of CO 335 00:15:35,560 --> 00:15:37,810 that we can ultimately see in the atmosphere. 336 00:15:41,280 --> 00:15:43,340 So in conclusion, and looking forward, 337 00:15:43,340 --> 00:15:45,980 convection-driven disequilibirum chemistry 338 00:15:45,980 --> 00:15:48,160 is a common feature of cold brown dwarfs, 339 00:15:48,160 --> 00:15:49,450 and by extension, we may see 340 00:15:49,450 --> 00:15:51,700 and directly image gas giant planets. 341 00:15:51,700 --> 00:15:53,650 Keep in mind that a lot of directly imaged plants 342 00:15:53,650 --> 00:15:55,750 are very young and have lower surface gravity. 343 00:15:55,750 --> 00:15:59,083 So convection may be a lot stronger in their atmospheres. 344 00:16:00,770 --> 00:16:03,170 And I won't talk about the figure a lot, 345 00:16:03,170 --> 00:16:05,840 but JWST Mid-IR observations 346 00:16:05,840 --> 00:16:07,340 will likely expand the types of molecules 347 00:16:07,340 --> 00:16:10,900 we can even see in the atmospheres of Y-dwarfs. 348 00:16:10,900 --> 00:16:13,310 And I know a lot of proposed missions, 349 00:16:13,310 --> 00:16:15,180 especially the large space observatories 350 00:16:15,180 --> 00:16:16,660 won't operate in the M-band, 351 00:16:16,660 --> 00:16:19,660 but this information is very complimentary to the gas giants 352 00:16:19,660 --> 00:16:22,340 you'll eventually image with HabEx and LUVIOR. 353 00:16:22,340 --> 00:16:23,173 And with that, 354 00:16:23,173 --> 00:16:25,383 I'll take questions, and thank you for your time. 355 00:16:27,900 --> 00:16:29,073 - [Mike] Thank you, Brittany. 356 00:16:30,010 --> 00:16:32,963 While people are mulling over a question, here we go, 357 00:16:33,830 --> 00:16:36,700 could you speculate on why convective mixing 358 00:16:36,700 --> 00:16:41,700 would give a CO signal for WISE 0855 but not phosphene. 359 00:16:42,640 --> 00:16:44,630 Would they come from different layers 360 00:16:44,630 --> 00:16:46,970 or is it a compositional difference? 361 00:16:48,210 --> 00:16:49,800 - [Brittany] Hold on. 362 00:16:49,800 --> 00:16:51,630 Actually, I shouldn't have stopped sharing. 363 00:16:51,630 --> 00:16:55,240 So that was, I still don't have the answer right there. 364 00:16:55,240 --> 00:16:57,030 I still don't have the answer about it. 365 00:16:57,030 --> 00:16:58,690 But one thing Caroline proposed 366 00:16:58,690 --> 00:17:00,690 was that phosphene is not present 367 00:17:00,690 --> 00:17:04,950 because it's contributing to another opacity source. 368 00:17:04,950 --> 00:17:06,600 And so there are certain clouds 369 00:17:06,600 --> 00:17:08,320 that can condense at a low temperature 370 00:17:08,320 --> 00:17:11,950 that may have phosphorus in their composition, 371 00:17:11,950 --> 00:17:14,193 but I don't have a good answer for that right now. 372 00:17:17,100 --> 00:17:18,460 - [Mike] And, to follow up, 373 00:17:18,460 --> 00:17:21,330 could you comment if having a first overtone, 374 00:17:21,330 --> 00:17:23,130 in addition to the CO fundamental, 375 00:17:23,130 --> 00:17:26,510 would this help you separate column densities 376 00:17:26,510 --> 00:17:28,040 or abundances and mixing? 377 00:17:28,040 --> 00:17:29,390 Can you pull the two apart 378 00:17:29,390 --> 00:17:32,030 to get C to O ratios, for example, 379 00:17:32,030 --> 00:17:34,873 if you had a broader wavelength range of data? 380 00:17:36,673 --> 00:17:40,020 - [Brittany] So can you define what you mean by overtone? 381 00:17:40,020 --> 00:17:45,020 - [Mike] So you're tracing the 4.6 micron CO fundamental. 382 00:17:45,920 --> 00:17:50,476 And then if you go up to the 2.3 micron features- 383 00:17:50,476 --> 00:17:51,680 - I see what you mean. - You're looking 384 00:17:51,680 --> 00:17:53,820 at a different temperature range of excitation, 385 00:17:53,820 --> 00:17:55,580 and then maybe that could help 386 00:17:55,580 --> 00:17:57,650 in pulling apart your Kzzs 387 00:17:57,650 --> 00:17:59,650 and your mixing from your abundances, 388 00:17:59,650 --> 00:18:02,250 which some of us would really like to know the abundances 389 00:18:02,250 --> 00:18:04,573 in addition to the atmospheric physics. 390 00:18:05,610 --> 00:18:07,610 - [Brittany] So I get what you're saying. 391 00:18:07,610 --> 00:18:09,430 The CO feature that I'm presenting now 392 00:18:09,430 --> 00:18:13,000 is not detectable at two microns across the K-band. 393 00:18:13,000 --> 00:18:15,310 I believe there's some ground-based K-band data 394 00:18:15,310 --> 00:18:18,450 of Y-dwarfs, and it's not exactly seen there. 395 00:18:18,450 --> 00:18:21,840 And then Joe Zaleski's 2019 paper 396 00:18:21,840 --> 00:18:23,430 also does retrievals on HST, 397 00:18:23,430 --> 00:18:25,580 and they can only get upper limits on CO from K 398 00:18:25,580 --> 00:18:27,070 for the near-infrared data. 399 00:18:27,070 --> 00:18:30,430 So I think we may have to figure out other wavelength ranges 400 00:18:30,430 --> 00:18:32,180 outside of the M-band to detect CO. 401 00:18:35,291 --> 00:18:36,391 - [Mike] Okay, thanks.