Mission/category:

Frequently Asked Questions
(last update: November 2, 2009)

Mission

Should I send technical questions to the MAST helpdesk?
Yes. For best service send questions on technical issues (i.e. not relating to the GO proposal program) to the MAST helpdesk at archive@stsci.edu. These will be screened within a work day and forwarded to the appropriate Kepler Project office if MAST should not or cannot answer them.
Can Kepler be pointed to observe another region of the sky?
No. The Kepler field of view (FOV) is centered on the sky position RA = 19^h22^m00^s and Dec +44^o30^'00^". This pointing will not be altered during the course of the mission.
Are there other sources of public information that describe photometric or spectroscopic observations of objects in the Kepler field?
Readers should consult the Related Sites page. We expect this list of links to grow with the mission as ground-based exoplanet hunters post their results.
What are the spatial properties of a point source on the Kepler focal plane?
The focal plane scale of the instrument is about 3.98 arcsec/pixel. Although Kepler is not meant to be an imaging instrument, each detector module has been focused independently. Some changes in focus and image quality are possible during the mission lifetime. According to the Kepler Instrument Handbook the goal is for 95% of the light ("Encircled Energy") to fall on an area of 7 pixels or less. Actual image characteristics may change subtlely from quarter to quarter, or even within seasons, because of differential aberration of starlight. Although this effect causes shifts no greater than +/-0.25 pixel, it can shift the distribution of flux among contiguous pixels. In its extraction of flux from the stellar image, the Kepler pipeline processing software should correct for this effect.
Where can I go to find recent status reports on the Kepler satellite?
NASA provides an official site for mission updates.The homepage of the Kepler Asteroseismic Science Consortium (KASC) also lists mission status activities of the satellite and data collection process. An Elapsed Mission Clock is furnished on this site to provide browsers of just where "today" fits into the mission lifetime.

Proposing

How do I determine what the schedules and writing instructions are for the next Guest Observer (GO) cycle?
NASA releases a ROSES (Research Opportunities for Space and Earth Sciences) document annually that announces the research programs its grants offices are supporting and the schedule and instructions for the proposal cycle. MAST recommends that users consult the official announcement at the NASA ROSES site.
Information from the GO office takes precedence over this response.
Other than late type stars that are planetary host candidates, does the Kepler Project reserve certain types of targets?
The Project's Science Utilization Policies document (soon to be released) states that the Project has selected about 1000 red giant targets for use in computing parallaxes for its other targets. An additional group of known eclipsing binaries, early type dwarfs, and cluster members have also been chosen. The "availability flag" of the Kepler Search form (see Catalogs section) will indicate these exclusions.
The GO office FAQ provides further information on interpreting rules governing availability flags.
Where do the targets on the Kepler Target Search page come from?
Objects visible on the Target Search page were provided from a list of objects, the great majority of which are stars, in the Kepler Input Catalog. See the question under "Catalogs" on the KIC.
Information from the GO office takes precedence over this response.
What is the procedure for proposing for extragalactic or other objects not returned in the Kepler Target Search results page?
GO proposers are referred to the Kepler GO program web site for information. In general, there is no prohibition on targets within the appropriate magnitude range. However, for extended objects the number of pixels required to cover an object is a limited resource for the Project. Proposers interested in proposing these types of targets should consult the Proposal instructions and FAQs for guidance in proposing such targets.
A FAQ from the GO target informs users of important consequences of requesting customized apertures, e.g. for extended sources.
What are the Kepler "seasons" all about?
Kepler was launched into an Earth-trailing heliocentric orbit of a little longer than a year (372.5 days), and this fact has a number of consequences. First, the spacecraft slowly becomes more distant from Earth. This fact ultimately places a hard limit on the mission lifetime. Second, in order to maintain orientation of the solar array toward the Sun, the satellite must roll on its pointing axis four times a year. Each of these intervals is called a season or quarter. The Project designates four seasons, numbered 0, 1, 2, 3, which repeat each year. New "quarters" start with the beginning of data collection for each new season and run continuously (1, 2, 3, 4, 5, etc.). The exception to this statement is that the Project has designated the commissioning period, ending on May 12, 2009 as "Quarter 0." This quarter has no analog in the seasons assignments. To find out the season start dates users may consult MAST's seasons table, See also the Quarter calender table under the Data Retrieval section. These tables will be updated as needed.
During a given season the CCDs are fixed in position such that light from any object in the FOV falls on the same group of pixels. Kepler's 42 CCDs (contained in 21 modules) have a four-fold symmetry such that when the satellite rolls 90^o a new CCD sees almost exactly the same area of the sky as an old one did during the previous season.
Information from the GO office takes precedence over this response.
Will the Kepler Project provide real data for proposers to play with?
The Kepler Project has released the light curve data for a number of targets observed during Quarter 0, the finalstage of spacecraft commissioning. See the dropped target list for a list of available targets. All users are free to download data for these targets. Publication of any research resulting from these data must have proper attribution and follow the MAST data use policy, which stipulates that they must wait until after January, 15 2010 before submitting results derived from these data for publication.
Information from the GO office takes precedence over this response.
How do I know if a given object is available for me to propose for the current GO cycle?
Search for the object in the Target Search Form. The numerical value of the "availability flag" will determine whether the object is available for proposing. At this writing only a flag value of 2 indicates a target restriction. It may be prudent for proposers to check with the GO office to see if justifications are required for objects that have been observed but are not formally restricted (i.e. objects with availability flag = 1).
However, note that whereas the catalog containing the Availability Flag is to be transmitted to MAST on an annual schedule, it is possible that stars may be dropped from the Project's list of key science targets more frequently. To address this contingency, GO proposers in the future should consult the Dropped Target List (referred to in the previous FAQ) to see if new targets are available for the proposal period.
Information from the GO office takes precedence over this response.

Data Retrieval

How do I retrieve Kepler data?
First, locate the data of interest, either proprietary or public, via the Kepler Data Search and Retrieval page (the page is currently not available). On this form specify one or more search criteria. Typical search selections are based on time of observation, target name (e.g., 2MASS id), proposal id (aka "investigation id"), stellar parameters, such as Teff, or target position in the sky. Note that kepler_id and target name are different identifiers. For standard target names the resolver (i.e., SIMBAD or NED) will return the target coordinates, which will then be used in the search. Uploads of target lists follow the same formats allowed for most other MAST missions. Lists are uploaded by clicking the File Upload form on the link at the upper right of the search page and selecting the list tab. See the Help for this form and the Kepler Archive Manual for further details.
Initiate the search by clicking on the Search button. The results of the search will be displayed.
To initiate data retrieval, click in the open box next to the desired data in the Search Results table. Proprietary observations are marked by a yellow strip and can be downloaded only by the Kepler Project PI for Key Project Data, the GO for GO proposals, and those collaborators for which the PI or GO have requested access via the archive helpdesk. Submit the list of data by clicking the "Submit marked data for retrieval" tab. Data retrieval follows in the same way as for the HST and FUSE missions. The retrieval Options page is displayed. The user may request the data be staged to an ftp area or sent directly to the user's computer. Either way, notification is sent by email when the process is completed. Anonymous retrieval is available for non-proprietary data only. Help on the retrieval options is available by clicking on any of the field option links. As of this writing the options for data products include light curve and pixel target files, in each case for whole Kepler quarters.
Problems and questions should be directed to the archive help desk at archive@stsi.edu.
How do I determine when the proprietary date for a target expires?
The date at which data become public will be visible to any user via the Kepler Data Search & Retrieval page when this page is released. If an observation is still proprietary, it will be color-coded yellow in the Results Table, and the release date will be in the future. According to NASA policy, the expiration date for Guest Observer data corresponds to one year from the date the data are archived or 6 months after the last data for the proposal is archived, whichever is later. If you are the PI and wish for an extension of this period, contact the Kepler GO office. If you are not the PI or CoI, and therefore do not have access privileges, be sure to recheck on the Search & Retrieval page to confirm the status as the date approaches to insure that the date has not changed.
For restricted Key Project data the proprietary date schedule is more complicated. The proprietary period starts with the start of science data collection for the Mission. A schedule of the expected release dates can be found in the following FAQ.
When does the proprietary period end for Kepler Data?
The table below lists proprietary periods for Key Project data. The period is given in months from the start of science data collection for the Mission and applies to the data taken during the specified quarter. A quarter is 3 months long. Be advised that the "start of science data collection for the Mission" and the "start of the first quarter" are assumed to be the same time. The periods in the table reflect the assumed 3.5 years mission lifetime and a 2 year extension. If the mission is not extended, all data are scheduled to be released after 54 months. Science data collection for the mission began on May 12, 2009.

Quarter Data Release Time

1 15

2 27

3 & 4 39

5 & 6 51

7 & 8 63

9 & 10 75

all data 84

For example, the current plan calls for Quarter 1 Key Project data to be released in the summer of 2010.
For Kepler non-Key Project data the proprietary period is 12 months from ingest of the data into the archive by the DMC. For GO data, the proprietary period is 1 year from ingest of the data into the archive or 6 months after the last data for the proposal are ingested, whichever is later.
Will the Project release any Key Project Data?
Key Project Data become public based on the schedule given in the quarters table, above. There are two additional ways for Key Project Data to be released:
o When the Kepler Team decides a Key Project target is no longer a planetary candidate, that target is dropped from the observing schedule. The existing data for that target will become public within two months of being dropped from the observing schedule.
o When the Kepler team publishes a refereed publication, the data supporting that publication are made public.
Why/when should I to register to retrieve data?
You should register only if you want to retrieve proprietary data. The system that handles the proprietary rights for Kepler data requires an archive account and password be entered before retrieving proprietary data. This will ensure that proprietary data are sent only to the GO or Kepler Team member authorized to retrieve the data.
Note that registered users must also be authorized to receive proprietary data.
Use the on-line form at http://archive.stsci.edu/registration to register (i.e., get an archive account and password).
The PI and GOs should request authorization for themselves and anyone else they wish to have access to their data when they register for their accounts. Only the PI or GOs may authorize someone else to access their data. If a Co-I wishes access to their data, he/she must have the PI or GO of the proposal send an e-mail to archive@stsci.edu requesting that access be granted. The email must contain the proposal ID number and the names of anyone who should be able to retrieve the data.
GOs and Kepler Team members may register as soon as they receive an investigation_id/proposal_id from the GO Office or the Kepler Project. You must register and be authorized before retrieval of your proprietary data will be successful.
What is the policy for public release of Full Frame Images (FFIs) and calibration files?
Full frame images (FFIs) are non-proprietary. Currently no FFIs have been released, pending detector characterization.
All calibration files, which are known as the Focal Plane Characterization Model, are expected to be public. Users should note that the calibration is applied across the field of view, not on a target by target basis. Thus the Focal Plane Characterization Model is applied to cadence data, not light curve or target pixel data.
May I request data over arbitrary lengths of time, assuming the data for that target is non-proprietary?
Yes, but be careful how the time is specified. Recall that light curves are produced on a quarterly basis. If the input start time in the query falls within a quarter, all light curves whose start times occur before the input start time and whose end times occur after the input start time, will be missed. For example, a query where start time > 26 May 2009 will miss all data with start times of 12 May 2009.

What are the start times for the Kepler quarters?
The planned start times for the Kepler quarters are given in the Table below. The planned end times are generally a day or two before the next planned start time.

Quarter	Planned Start Time
1	May 12, 2009
2	June 18, 2009
3	Sept 17, 2009
4	Dec 17, 2009
5	Mar 22, 2010
6	June 24, 2010
7	Sept 23, 2010
8	Dec 22, 2010
9	Mar 28, 2011
10	June 27, 2011
11	Sept 29, 2011
12	Dec 29, 2011
	Apr 2, 2012
14	June 28, 2012

How do I find public data in the archive?
To find public data in the Kepler archive, go to the Data Search and Retrieval page. In the "Release Date" field on this page, enter the less than sign followed by the current date in the form MMM dd YYYY. For example < Oct 30 2009. The results page will show all Kepler data with a release date prior to the current date. By definition, these data are public.

Catalogs and Search Pages

What is the "KIC" and how does it relate to what I see on the MAST/Kepler search pages?
The KIC, or Kepler Input Catalog, is the primary source of information about objects observed as part of the ground-based Kepler Spectral Classification Program (SCP) in preparation for the selection of Kepler PI and GO targets. The KIC lists objects down to 21st magnitude, but it is not complete to this limit. Light from only about 1/3 of these objects falls on the Kepler CCD detector. A small number of the KIC objects are calibration objects distributed across the sky. For this reason the full KIC should never be used for Kepler target selection. (By "target" we mean any fixed celestial object observable by Kepler). Information from the KIC is combined with data in two other catalogs to allow searches on the Kepler Target and Data Search pages; see next FAQ.
MAST provides a portal to those who want to see the contents of the full KIC. Also, Release Notes for this compilation have been posted by the SCP team. A gzipped pip-delimited ASCII file of the entire KIC (including 3 fields added by MAST) is available for download.
Are there other Kepler catalogs delivered to MAST?
The Project delivers to MAST the Kepler Target Catalog (KTC) and the Characteristics Table (CT). The KTC is basically an observing log, containing both the observed and planned targets. This catalog is delivered to MAST quarterly. The CT contains object-specific information pertaining to the Kepler objects, such as the column and row pixel location. The CT is to be redelivered annually. Access to information in these catalogs is via MAST's Kepler Search and Retrieval page and Kepler Target Search page. See the on-line help, available on these pages, for details.
Are there objects visible to the Kepler detectors that are not in the KIC?
Yes. The KIC includes objects as faint as 21st magnitude, although its coverage is not complete to this brightness level. In particular, variable sources and extended sources with low surface brightness may not be in the KIC because they were not in the ground-based catalogs that were used to make it.
The "Galaxy/star" flag (range = 0 to 1) provides a limited identification of extended objects. However, users are strongly cautioned against assuming this indication is accurate as a clump of stars can be flagged as extended.
What are the objects with kepler_ids greater than 100,000,000?
There are two types of objects with kepler_ids greater than 100,000,000. The vast majority are CCD monitors, which are engineering targets defined by the Kepler Project. The remainder are astronomical objects that have been or will be observed by Kepler, but which do not appear in the KIC, or groupings of KIC objects that can not be adequately resolved by Kepler. Examples include faint flare stars, planetary nebulae, and subclusters of stars. The Project is expected to provide positional information, only, for these objects.
What is the Kepler magnitude?
The "Kepler magnitude" is a magnitude synthesized from Sloan-filter colors observed in the SCP program. For late type stars it has an equivalent wavelength of about 6000 Angstroms (discounting color effects in hot and cool stars). Note that the Kepler magnitude has nothing to do with fluxes observed by the unfiltered Kepler instrumental system. The SCP documentation on the KIC, and the FITS keyword in the light curve headers use the word KEPMAG. MAST has followed this nomenclature.
What is the Spectral Classification Program (SCP)?
Early on, the Kepler Project realized the need for homogeneous ground-based observations that would provide information about all the stars in its detector's field of view. The SCP, a project commissioned to the Harvard-Smithsonian Center for Astrophysics (led by Dr. D. Latham), realized the solution to this need by providing colors from copies of the filters used for the Sloan survey (plus an additional "metallicity" filter). A copy of the SCP plan is available. The colors and color-derived quantities shown in MAST's Kepler search pages are derived from this program. In addition to this photometry the SCP included high dispersion spectroscopic observations of several thousand stars. Quantities from that program will eventually be exported to another site, and MAST plans to link to them when they are available.
How do I search for an object by RA in decimal hours?
The Kepler search forms have fields for entering Right Ascension and Declination but they only accept decimal degrees or sexagesimal (hhmmss) formats. To search for RA in decimal hours, go to one of the "user-specified field" pulldown menus, select the entry "RA_hours (J2000)", and then enter values in the corresponding "Field Descriptions" box. Note that currently the File Upload search option accepts only RA in decimal degrees or sexagesimal format. For more help, click any of the form element labels on the search form.
Note that the coordinates in the search results will always be displayed in sexagesimal format unless one clicks the "Hours" button in the "Output Coords" field element.

Data Handling, Analysis, and Quirks

What are the exposure times of short, long cadence time series data?
Following the terminology given in the Kepler Instrument Handbook, the interval between reads of a given pixel on a CCD is called a "frame" (equivalently an integration time). The integration time consists of the "exposure time" (accumulated time of flux from a celestial source on the pixel), 6.02 seconds, plus a fixed read out time of 0.52 seconds. The default exposure time for a short cadence is thus 6.02 x 9 or 54.2 seconds. The cadence rate or integration time, is (6.02 + 0.52) x 9, or 58.9 seconds. The default exposure time for long cadences is thirty times 54.2 , or 1626 seconds. The cadence rate between starts of consecutive integrations is thirty times 58.9, or 1766 seconds.
What kind of time series (light curve) data product is the Kepler Project planning to release?
For at least the first year the Project is producing a light curve using a "simple extraction analysis." In the following year or two the Project plans to release two new products, both "optimal extraction" and "differential analysis" techniques. No details on these techniques are available at this writing.
Information from the GO office takes precedence over this response.
In what units are the time series light curves given?
The time units are seconds (SI). The "flux" units are "electrons per cadence" and may be thought of as an instrumental flux unit closely approximating a linearized unit (for unsaturated pixels). Currently there are no plans for the Project to produce a product in a calibrated absolute magnitude system.
Information from the GO office takes precedence over this response.
UTC, barycentric time, MJDs, etc. - What does Kepler use?
There are several FITS keywords in the Kepler data headers that relate to time. A good rule of thumb is the times in the primary header will be UTC (geocentric), while the times in the extension headers will be barycentric dynamical time (TDB). It is expected that times related to processing, such as when the FITS file was created or when the processing was completed will be in UTC. Times related to the data in the FITS file will be in TDB.
NB: By definition, TDB includes a relativistic correction. This is a periodic term, which may be as large as 1.6 milliseconds. The yearly average of the periodic term is zero (0). However, currently the relativistic correction is not included in any of the Kepler data.
As of this writing, Modified Julian Date (MJD) is a common unit for the time. In the initial November data release, barycentric time corrections have not been applied.
What is the reference time for Kepler data?
For Kepler, the reference time is the end time.
In the Kepler Instrument Handbook, Section 7.3, users are warned against assuming a precision of better than 9.0 seconds in the absolute time.
The Spacecraft Clock, known as the Vehicle Time Code (VTC), has a time resolution of 3.9 milliseconds.
For further details consult the Kepler Instrument Handbook, which will be released shortly.
What are target pixel files? Are they the same as cadence files? When will I need them?
Target pixel files are target-specific, binary tables that list the original (uncalibrated) and calibrated pixels values for the target. They are created at the Data Management Center (DMC) at STScI from the calibrated cadence data. These files are provided to permit users to perform their own calibration steps if they are not happy with the calibration done by the SOC. Users are advised to consult someone with intimate knowledge of the Kepler pipeline processing algorithms before embarking on do-it-yourself analyses.
Note that target pixel files are not the same as cadence data. Target pixel files are target-specific, while cadence data contain the pixels for every target.
Target pixel data headers contain a number of exposure related keywords that are not in the light curve headers. NB: As target pixel files are created from the cadence data, not the light curves, there may be some difference in the exposure time.
Which FITS header keyword tells me the actual exposure time?
There is no exposure time keyword in the light curve headers.
The Kepler integration time is composed of a fixed exposure time plus a fixed readout time. The exposure time for science data is 6.02 seconds, while the read out time is 0.520 seconds, for an integration time of 6.54 seconds per pixel. Individual reads of each pixel are summed on board before being written to the recorder. Long cadence data are summed for 30 minutes, (270 integrations) while the short cadence data are 1 minute sums (9 integrations), yielding total per pixel exposure times of 1625.4 seconds and 54.18 seconds,respectively.
The target pixel file contains some exposure keywords, which are listed here.
EXP_TIME= exposure time (seconds)
READTIME= read out time (milli-seconds)
INT_TIME= integration time (seconds) (exp + readout time)
NUMSHORT= number of integrations in a short cadence frame
TEXP_SC = total short cadence exposure time (seconds)
TREAD_SC= total short cadence readout time (seconds)
TINT_SC = total short cadence integration time (seconds)
SHRTLONG= number of short cadences per long cadence
TEXP_LC = total long cadence exposure time (seconds)
TREAD_LC= total long cadence readout time (seconds)
TINT_LC = total long cadence integration time (seconds)
Which FITS header keyword tells me how many pixels were used to determine the aperture for observing an object? Which tells me how many we actually used?
At present there are no keywords in the light curve or target pixel file headers that provide this information. A request has been made to the Kepler Project to have the number of pixels used added to the light curve header.
The target pixel data header contains the keyword APER_ID, which gives the aperture used. However, there is no keyword indicating how many pixels make up the aperture or how many of those pixels contribute to the light curve.

Multiwavelength Surveys

Did the Sloan (SDSS) project survey the Kepler field?
No. The Sloan Survey covered 1/4 of the sky outside the Galactic plane and did not include this field. To simulate the results of the Sloan survey the SCP team observed KIC objects with a set of Sloan-like filters. The KIC catalog is comprised in part from data taken from this program.
Has the GALEX project surveyed the Kepler field in the near-UV and far-UV?
In the summer of 2009 the GALEX Project surveyed about 1/4 of the Kepler field. These survey products will be added to the GALEX GR6 (General Release 6) in early 2010. These products will be available via the MAST/GALEX website.
Are there other UV-optical-IR missions that have surveyed the Kepler field?
The 2MASS Survey, a survey of 70% of the full sky at the 3 infrared J, H, K bands (1.25, 1.65, and 2.17 microns), includes nearly all bright KIC targets, and is fairly complete down to KEPMAG 16 or 17. For all but faint KIC objects the 2MASS_ID often provides a good (though imperfect) substitute for Kepler_ID values in queries on the MAST search pages, particularly for cross-referencing to external catalogs.
Users should be also aware of objects observed from the ground in the Kepler All Sky Automated Survey. This is a photometric survey dedicated to the ground-based study of optical variables in the whole observable sky (both hemispheres), including the Kepler field.
Does the Digitized Sky Survey cover the Kepler field?
Yes. Go to the Google Sky site and enter the following in the string: http://keplergo.arc.nasa.gov/tools/KeplerFOV.kml to see the location of the Kepler CCD "footprints" against a Digital Sky Survey map of the sky. (Courtesy of a tip on the Kepler GO website.)

Documentation

Is there a handbook that describes resources at MAST for astronomers to investigate or propose for Kepler data?
Yes there is. The Kepler Archive Manual provides a description of MAST and its resources.

Frequently Asked Questions(last update: November 2, 2009)

Frequently Asked Questions
(last update: November 2, 2009)