Plot 1 - Sample Plot Alt Text
This plot aims to show the sample for the APO-K2 catalog as it appears on the sky. The plot is rectangular shaped with the x-axis about twice as long as the y-axis. The x-axis shows the Galactic Longitude, in units of degrees, between -150 and 150 degrees with 0 in the center of the x-axis. Similarly, the y-axis shows the Galactic Longitude, also in units of degrees, ranging from -75 at the bottom to 75 at the top; again, the center of the axis is 0. Both of the axes have text axis labels with 'Galactic Longitude (Degree)' on the x-axis and 'Galactic Latitude (Degree)' on the y-axis. None of the corners of the plot have numbers attached to them and the true scale of the x- and y-axis are a little more and a little less than the numbers stated.
There is a colorbar to the right-hand side of the plot, with vertical text reading 'Fe/H', corresponding to the metallicity of the stars shown in the plot. The scale runs from -1, right at the bottom of the colorbar, to 0.4 at the top, although the scale runs to 0.5. The lowest metallicity stars (at -1.0) correspond to a deep purple, this moves up through blue, teal, green, to yellow (at 0.5).
The plot itself shows a background of the Galactic plane, with the Galactic center at 0,0, in the center of the plot, and the Milky Way running from the left to right across the plot. The top and bottom of the image are black, corresponding to space outside the Galactic plane. As the y-axis moves closer to 0 at the center there is a line of dust, gas, and light as we reach the Galactic plane. The small and large Magellanic Clouds are seen to the bottom right of the Galactic center, about a third of the way between the plane and the bottom of the plot.
Overplotted on the background are the K2 campaigns, made up of points of color representing separate stars. Each campaign, loosely takes the shape of a Kepler field, which looks like an off-angle square with each corner having a smaller square removed. Each of the small points representing stars are colored consistent with their metallicity, represented by the colorbar.
The campaigns run from the left-hand to right-hand side of the plot, mostly equally spaced (with some overlapping) in the shape of a sine curve flipped on the x-axis. On the left, just below the Galactic plane are the campaign 13 stars, mostly made up of teal, slightly sub-solar metallicity stars. Campaign 13 is half off the plot, the other side of it being shown on the right-hand side. Overlapping the bottom right-hand corner of campaign 13 is campaign 4. Both oriented so that the Kepler 'square' looks more like a diamond. Further below the plane and to the right is campaign 8, which is darker blue than the previous two. To the right of this, and at around the same Galactic latitude is campaign 12 and just above this to the right is campaign 3. These are both roughly the same color as campaign 8, but are closer together. As the reflected sine curve starts to curve upwards toward the Galactic plane, we get to campaign 7, which is sparsely populated, and with a generally higher metallicity. It appears to be the least populated campaign that shares no overlap with other campaigns. As we move through the Galactic plane in the middle of the plot, we see campaign 11, above this is campaign 2, and above this is campaign 15, all on a diagonal upwards toward the right. These campaigns all overlap, are relatively sparsely populated, and have fairly metal-rich stars (relative to the rest of the campaigns). Above this to the right, and out of the Galactic plane, we see campaigns 6 and 17, with 6 underneath and 17 directly above, almost completely overlapping. These have similar metallicities to campaigns 8, 12, and 3, and are at similar distances above the Galactic plane, as the aforementioned were below it. Next, almost at the same Galactic latitude but reasonably spaced are campaigns 10, 1, and 14, each more populated than the last and with low metallicity overall. Finally, more towards the galactic plane, but still above it, are campaigns 16, 5, and 8, which all overlap and show relatively low metallicity.
Just above the Galactic plane, about half way between the left-hand side of the plot and the Galactic center is the Kepler field, showing a relatively high metallicity when compared to the majority of the K2 campaigns. It is the most populated on the plot, as all CCD modules are working in this mission. Each campaign, and the Kepler field, are labeled with white text with their campaign number as C followed by the number. The Kepler field is also labelled as 'Kepler'.
Plot 2 - Mass-Radius Selection Function
This figure comprises four plots which describe how the selection function of our catalog compares to the Galactic distribution in the mass-radius space. The description of how these plots were made can be found in the text of the paper, as can the discussion of the conclusions drawn from the plot. these four plots are arranged in a two by two grid, with the two plots in the first row representing density maps, and the bottom two showing histograms. The plot on the top left is a density plot of the relative density of mass (x-axis) and radius (y-axis) between the K2 observed and simulated samples. The mass axis has ten evenly spaced ticks on the x-axis, reading from left to right, with values of: 0.10, 0.30, 0.5, 0.70, 0.90, 1.10, 1.30, 1.50, 1.70 and 1.90 M_sun. The y-axis also has 10 evenly spaced ticks, from bottom to top, they read: 3.40, 6.20, 9.00, 11.80, 14.60, 17.40, 20.20, 23.00, 25.80, 28.60. The title of this plot states 'N_k2-GAP/Nimulated' to describe what the density plot is showing. The second line of the title reads N_k2-GAP = 95503 -- N_simulated = 538414 to show how many total stars are in the samples that create this plot. The x and y axes are labelled accordingly and a colorbar is placed on the right hand side, vertically, from deep red at the bottom, through white, to deep blue at the top with equally spaces ticks of -2 at the bottom of the color bar, through 0, to 2 at the top. The colorbar is labeled D_hat for the scaled density and the more blue a box appears the more K2_gap stars are in the bin, the more red the box appears the more simulated stars are in the bin, these colors are labelled as such. Within the density plot itself, the first colomn is comprised entirely of grey bins, as there was no relative density value in this space. The next column contains one deep blue pixel, showing that there are more K2-observed stars in the bin containing stars with ~23Rsun and ~0.30Msun. The next colomn has 6 bus colored, mostly dark blue. The remaining bins are also, all colored, showing that each of the bins contains a relative density. In the top right area of the density plot there are a number of red bins, which are all similar shades of red so that they seem to blend together, indicating that there are roughly the sample value of relative density in each bin, favoring the simulated stars. Moving toward the higher mass and smaller radius stars, we see a white, and off-white, diagonal strip of bins reaching from the bottom left to the upper right, demonstrating that these bins have roughy the same amount of stars in both sample. Below this diagonal line there are more blue bins, indicating more stars in the K2 observed sample than the simulated sample. In the smaller radius regime there is a mix of blue and red bins, therefore, some of the bins have more k2 observed stars and some have more simulated stars.
The plot on the top right takes on the same structure, with the same tick numbers, x- and y-labels and colorbar. Although in this case, the colorbar ranges from dark blue at the bottom to dark green at the top, where blue represents an abundance of k2 observed stars and green represents an abundance of APO-k2 stars. The title reads, N_apok2-Nk2-gap on the top line and Napok2 = 8460 -- Nk2)gap = 13722 on the bottom line. The plot itself looks slightly different to the density plot to the left. The right half of the plot is dominated by light blue bins (apart from the bin the bottom right corner, which is grey and not populated). These blues are fairly similar to themselves, suggesting a similarity in this parameter space of relative density between APOk2 and K2gap. Towards the left hand side of the plot there is a mixture of grey, blue, off-white, and green bins, but mostly green, signifying an abundance of APO-K2 stars relative to the K2 observed stars. In particular in the area of smaller radii and lower mass there is a 'bump' that juts out with almost entirely dark green pixels.
The bottom two plots are histograms, each representing three samples of data, overlayed by three histogram lines with 100 bins each. The left hand histogram shows the number of stars in a log scale on the left, labelled N. This axis starts at the bottom at 0, and extended to greater than 1000. The x-axis spans from 2 - 30 R_sun, and is labelled as such. The range of radii is shown as text on the bottom left hand of the histogram. In the top right there is a legend that shows the color representing each sample. The red line shows the simulated sample, the blue line shows the K2 observed sample, and the green line shows the APO-K2 sample. The red line is above all the other lines, with the most stars in the sample. It initially starts with a sharp upward vertical line, where the cut in the sample has been made, it then gradually shows a small hill in the small radii before increasing rapidly into a peak that drops just as rapidly, around R ~10Rsun. This peak corresponds to the red clump. After the decrease in number comes a slow decline in the line to the high radii and a sharp vertical line at 30 representing the cut. Both the green and blue line fall under the red line, but hold generally the same shape. Both start with the straight vertical line representing the cut in the sample, followed by a much smaller bump representing the red clump stars, although nowhere near as sharp as the simulated line. The decline after the clump peak is steeper in these samples, with the blue line in between the red and the green line is the steepest. The green sample (apok2) is sparsest in the high radii regime, where small individual peaks, that look somewhat like a skyline, pepper the high radii area of the plot.
The bottom right histogram uses the same three colors to represent the sample as the bottom left plot, and the y-axis remains the same, with the same label and tick marks and labels. The x-axis is the stellar mass, in units of solar mass and this histogram ranges between 0 and 2. In this case the left hand side of the plot is dominated by both the green and blue histogram lines, overlapping and showing small spikes and overlapping one another. This are of relatively sparse for these samples. The red line, showing the simulated sample however, stars at around 0.4Msun and lowly starts to rise, before peaking just before 1M-sun, it plateaus and then slowly descends toward the right hand side of the plot. The blue and green lines follow roughly the same pattern with the red line above the blue line, above the green line. Between roughly 0.6 and 1Msun, the blue line dips under the green line.
Plot 4 - Mass-Radius Selection Function
This plot has the same layout as the selection plot shown in Plot 3, and the layout description given in the alternative text for that set of plots Plot 3. In this case the parameter space is mass vs. metallicity and on both top plots where the x-axis, labelled with mass M_sun, have 10 ticks labelled as follows: 0.44, 0.92, 1.40, 1.88, 2.36, 2.84, 3.32, 3.80, 4.28, 4.76. The y-axis is labelled Metallicity [dex] and has tick labels, from the bottom to the top as follows: -2.35, -2.05, -1.75, -1.45, -1.15, -0.85, -0.55, -0.25, 0.05, 0.35. The title of the top left lot is Nik2-gap/Nisimulated on the first line and Nk2-gap = 95503 -- Simulated = 545374 on the second line. The color bar of the left hand top plot is the same as the colorbar on the top left of plot 3.
In the to left density plot, there is a large grey area in the bottom right quadrant of the square. The colored bins populate the the relative high metallicity area of the plot and the low mass area. The colored bins of the plot form a upside down L shape in in the density plot. The majority of the bins are red, showing a higher relative density of simulated stars. However, there are majority blue bins in the third column and at some of the more solar-like metallicities. Forming what looks like a bimodality in the plot. The right hand density plot is more populated, but with grey bins to the right bottom corner of the plot. The majority of the plot is blue, showing more k2 gap stars relative to the APOk2 stars. The low mass area of the plot is mostly green.
The histograms at the bottom of the figure have the same color and N scale as the previous figure. The left hand histograms represent the metallicity in the sample. The metallicity scale is from -2.5 to 0.5 from the left to the right. The red line, showing the simulated stars, shows a bimodal distribution with a peak on the left and on the right, with the peak on the right is the highest. The drop in the middle of the bimodal distribution sinks below the blue and green lines. The blue line and green line follow the same general trend as one another, starting with a slow incline, towards around -1 and then a sharper incline followed by a sharp descent, after peaking around -0.5. In the low-metallicity regime of the plot, the blue and green lines are less populated with the bins having various heights and the lines overlapping with one another. The blue line is higher than the green line until around 0, when the blue line drops quicker than the blue. The second histogram shows the mass between 0 and 2 solar masses. All of the lines follow roughly the same shape, with a sharp increase to a peak at 1, and then a slow decrease to the right hand of the plot. The red line (simulated sample) is higher than the other two other lines. The only exception to this is at masses less than 0.5, where the red line dips below the green and blue lines. The blue and green lines mostly overlap until around 1 solar masses and then the blue line is higher than the green line. Around 3 solar masses there are sparse amounts of stars in the apok2 and k2 sample, where small peaks and troughs appear in the apok2.
Plot 5 - Color-Magnitude Selection Function
This plot has the same layout as the selection plot shown in Plot 3, and the layout description given in the alternative text for that set of plots Plot 3. In this case the parameter space is color (x-axis) and magnitude (y-axis). The tick labels on the x-axis (from left to right) are 0.45, 0.54, 0.62, 0.72, 0.80, 0.90, 0.99, 1.08, 1.7, 1.25. The tick labels on the y-axis (from bottom to top) are 15.50, 14.50, 13.50, 12.50, 11.50, 10.50, 9.50, 8.50, 7.50, 6.50. The left hand plot title reads: Nik2gap/Nisimulated on the first line and nk2-gap = 110962 -- Simulated = 1109620 on the second line. In this density plot the top two rows are greyed out; the majority of the rest of the bins are populated, apart from a few on the third row, and two in the bottom left corner. The majority of the plot, mostly toward the center is off-red, off-blue, or white, meaning the there are reasonably similar amounts of stars in both samples. The right-hand plot has more grey, with the first three rows from the top and the majority of the fourth row are greyed out. The bottom half of the plot is mostly populated, with one of two bins greyed out. The center of the colored area is mostly green, with a larger amount of relative APOk2 stars, the green area is surrounded by off blue and off green bins and then surrounded again by blue bins. The bottom row of histogram has the same scaling and color as the previous plots, the left hand plot shows the color between 0.4 and 1.3 in J-K. The blue and red histograms are very similar. They both show a sharp increase on the left hand side before a slow decline toward the left hand side. There is a small increase, in the shape of a bump at around 0.8. The blue line vertically descends at around 1.2 and the red line vertically descends a little later, at around 1.3. The green line is about half way down the plot, underneath both the red and blue lines and shows a quick increase followed by a slow decline. At the left-hand area of the plot the red line is the first to be populated, followed by blue and then green, in a messy slow increase. The right hand plot corresponds to the color of the stars in the samples and ranges from 8 to 16. In this plot the blue and red lines almost exactly overlap, with very little change between them; after a small initial bump and decline there is a vertical increase to about 100 followed by a slow increase to a peak at around 14, where the samples top out at around 3000 stars. The is then a step like decline followed by a vertical drop off where the sample is cut at 16. As with the left hand plot, the green line is under both the red and blue histograms and forms an almost perfect semi-circle, as rising sun from the x-axis, with this exception of a more sudden increase on the left hand side, at around 9.
Plot 6 - Magnitude-Numax Selection Function
This plot has the same layout as the selection plot shown in Plot 3, and the layout description given in the alternative text for that set of plots Plot 3. In this case the parameter space is magnitude (x-axis) and numax (y-axis). The numax is corresponds to the frequency of maximum power for the star. The x-ticks are, for numax, from left to right are: 8.40, 9.20, 10.00, 10.80, 11.60, 12.40, 13.20, 14.00, 14.80, 15.60.
Plot 2 - H-R Diagram Alt Text
Almost two square plots side by side. Both have the same x- and y-axis with roughly the same limits. The y-axis is labeled Luminosity [L_sun] and the scale is in a log-space from 0 to ~400. The x-axis is labeled Effective Temperature [K] and is on a linear scale ranging from just below 5400 K to above 4200 K. None of the numbers are explicitly on the corners of the plots, and these limits vary slightly over and under the tick labels. There is a colorbar to the right of the two plots labeled [M/H] and shows the metallicity of the stars from just below -2.0 at the bottom up to just above 0.5 at the top. The colors scale ranges from white to dark blue, following through hues of blue on the way. The filled circles are all outlined in black, so that the low metallicity stars can be seen on a white background.
The plot on the left has a title stating 'Red Clump Stars: 2446' and a legend in the bottom left corner, indicating that cross markers represent the red giant stars and filled circles correspond to the red clump stars. The filled circles are far more prominent on the plot as these are the stars we want to show. The crosses lie under the filled circles and run from almost the left-hand corner of the plot to the top right. They have a width corresponding to around 200 K and this gets slightly thicker as the sequence moves to the top right. The crosses are roughly evenly distributed, although a clump of them is visible under the bottom filled circles. This corresponds to the red bump stars. The filled circles indicating the red clump stars start about half way across the plot, and about half way up the sequence of crosses. The majority of the points form almost a triangular shape, fanning out towards the left-hand side of the plot. These points are more dispersed at the upper and lower areas. They are a collection of hues, with the darker points (corresponding to more metal-rich stars) more towards the center, and the more metal-poor stars generally towards the middle and left-hand side of the red clump. There are a few stars removed from this fan shape, further towards the left-hand side of the plot. The larger stars (indicated by the size of the points) are towards the top of the plot and the top left, with the smaller stars in the clump or on the right of it, overlapping with the crosses. There is a collection of stars below the fan shape, indicative of the secondary red clump. Next to the legend at the bottom of the plot is a text box stating 'Point Sizes Indicative of Stellar Mass [M_sun]', and next to this is a representative error bar for the red clump stars, with spans ~10K in temperature and a couple of solar luminosities.
The left-hand plot shows the same as the right-hand plot, but in reverse, with the crosses indicating the red clump stars from the left-hand plot and the points representing the red giant stars, shown as crosses on the left. There is a similar legend in the bottom left corner showing that crosses are indicative of red clump stars and filled circles are indicative of red giant stars. There is also an error bar in the bottom right corner of the plot showing a smaller error for both luminosity and temperature for these stars. For the points themselves, the sequence is the same as described above but now the color and size of the points is evident. There is a larger abundance of metal-poor stars towards the warmer edge of the sequence. There is a clear edge to the sequence on the right with more scattering on the left, and a couple of points dotted about to the top right and to the right of the sequence. The bottom of the sequence is also very sharp. The sizes of the points are less varied that on the Red Clump plot but do show high mass stars toward the top left. There are also low metallicity stars in this area. The title of this plot reads 'Red Giant Stars: 4053', indicating the number of stars in the red giant sample shown on this plot.