TIGar: the archive of TIGRE

TIGar Help

Menu:

• Help
• TIGRE Home
• TIGRE Weather
• TIGRE Users
• S/N Calculator

TIGar Help

Users

There are three types of users:

1. Astronomers from the University of Hamburg, Guanajuato or Liège: they may register at any time and can be PI (1) of projects.
2. Astronomers from other institutes that are CoI from a project. They are automatically invited to register and they can then retrieve the observations. They are not allowed to be PI of a project, only CoI. Also, only if they have been invited, they can register.
3. Guests: they can make searches on the archive and contact the PI if they are interested in the observations.

Registration

Before you can use the Archive, you have to register in the system. In the registration you give your personal data (name and e-mail (2)), your Institute and the username and password that you want to use in the archive. Users and passwords should be at least 6 characters long.

Once you have registered, you will receive an e-mail with a confirmation code and a link. Please, follow the instructions included in this e-mail to confirm the registration. Without this step your are not completely registered. This is done in this way to avoid that someone register using a false e-mail address.

Proposal

When you write or edit a proposal, you can save or send it by clicking in the buttons on top and bottom of the page. With "save", the proposal is stored and will be yet edited. If you click on "send", it means that the edition of the proposal is finished and the proposal will be taken into account by the Scheduler of the TIGRE after the Scientific Manager of the Archive has approved the proposal. Please also see note (2) for the e-mail address of your Co-I.

The scientific and technical justification is the pdf file of the proposal that you have earlier sent to the institute board members.

The list of targets of the proposal contains buttons to "edit", "remove", "copy" and "list Spec" for each target. The "copy" button clones the target, so that you can edit the new one: in this way the introduction of many similar targets is simplified. Once the TIGRE has taken spectra of the target, the "list spec" button is activated and will give you a table with the observations performed (see below -link section table--).

Target

Object characteristics

If you introduce the target name and then click on the "simbad search" button, this target name is searched on Simbad and the parameters of the star are automatically written on the form.

Please, take into account that the B and V magnitudes are used for the automatically selection of the filter and exposure time in the guiding process and they are necessary for the exposure time correction (see (3)). Therefore, if you introduce false values or no values, then it is possible that the target will not be detected. The values shouldn't be very accurate (an error of 0.1-0.2 mag is enough), but reasonable. Also, if your target is a strong variable, consider to actualize periodically the magnitude values here.

The coordinates can be written in decimal format (dd.ddddd) or in sexagesimal format (dd:mm:ss.ss / hh:mm:ss.sss).

The proper motions in RA and Dec should be written in milliarcsec/yr.

Click on the button is NOT the brightest in the field if your star is not clearly the brightest in the field of view of the guiding camera (2.5'x2.5'). Otherwise, it is possible that your target is not acquired, but the brightest seen by the guiding camera.

The target priority is the priority of the target inside the project. Typically it will be 1 for all of your targets, but you may have targets that are more important than others.

Individual TIGRE visit (may be composed of several exposures)

A TIGRE visit comprises the successful acquisition of a target and one or more subsequent exposures, which TIGRE carries out without leaving the target.

The TIGRE target-specification form provides two options for structuring a visit:

1. a fixed number of exposures with fixed duration and
2. a minimal S/N requirement.

In the first case, TIGRE will consecutively carry out the specified number of exposures, each with the given exposure time. To determine reasonable exposure times, the "exposure time calculator" may be consulted. If a minimal requirement on the S/N ratio is specified, it is mandatory to define the reference wavelength for the S/N calculation; note that the estimate refers to the continuum and with binning=1. Additionally, it is advisable to suggest a number of exposures and an estimate of the exposure time, e.g., based on the output of the TIGRE exposure time calculator (see note (3) for further information).

In the very special case of targets that have a very red color, you can request for different exposure times in the blue and the red channel of the spectrograph. In this way, you can avoid saturation in the red channel spectrum, while having a good exposed spectrum in the blue channel. Please note that the number of exposures will be the same for both channels. If you want this option, simple write both exposure times (in seconds) separated by a comma (texpB,texpR). Please justify why you request this option.

In the case of very long total exposure times, e.g. monitoring the target during the 4 hours, there were problems by the selection of the target, when the time available was less than the total exposure time. Previously, the observation were splitted in several ones, which included the whole movement of the telescope and the start of the guiding process; therefore some time were lost. Now you can select the "Minimal total exposure time(s)/visit", as the minimal total time that is useful for you, and the target can be selected as long as so much time is available. This is recommended for total observation time larger than 2 two hours. If this field is 0, then the total exposure time (number exp. x exp. time) will be used by the scheduler for the selection of the target.

By default, the TIGRE pipeline produces one spectrum per exposure. If a visit is divided into more than one exposure, the reduction pipeline can combine the spectra, so that a single, merged spectrum per visit is produced. Check the associated flag to request that reduction option.

Observing strategy

TIGRE visits must be arranged into "observing groups", which may comprise one or more TIGRE visits. In the "observing strategy" section you are asked to specify the observing groups and, thus, the desired temporal distribution of the requested TIGRE visits and further time constraints if necessary. For each group of observations you may enter a start- and end-date (both optional). These dates can be given as JD or in the format yyyy-mm-dd hh:mm:ss. In case of time critical observations, e.g., for simultaneous observations with other observatories or satellites, please check the corresponding mark.

If no special constraints have to be specified, you should indicate the required number of visits and the minimal interval in days between the visits (this value is optional; 1 day is the default value).

For monitoring observations, you should specify the number of visits (optional) and the desired interval in days between them.

For each object, more than one group of observations may be defined. In this case, the minimal and maximal time-span between the individual groups may be given (optional). Please note that the visits and, thus, exposures belonging to the second (or next) group of observations does not start unless the observations of the previous group are finished.

Click on ToO if the observations requested are a target of opportunity. ToOs are specially considered by the scheduler and the observations will be obtained as long as the they are possible. Please, justify in the comments or in the scientific justification why this is a ToO.

Examples:

• Simultaneous observations with a satellite: introduce in the start and end date when you want the observations, click on the button for ToO observations and select which is better: no constraints or monitoring. If you want only one observation during in the period selected, choose no constraints, number Obs=1. If you want that during the time period selected the TIGRE telescope observes continuously your object, you can select monitoring with an interval shorter than the exposure time.
  For more simultaneous observations of this target, click on AddObsGrp and give the corresponding values.
• Long term monitoring of a target. Simply choose the monitoring option, and give the desired interval. Leave blank the fields for star and end date and the number of observations.
• If you want daily observations during a week and then one observation per week during 3 months: select monitoring for the first group, with number Obs=7 and interval=1. Then for the second group, select also monitoring with number Obs=12 and interval=7. Then the minimum time span between the groups should be 7 days.

Others

Please click on the corresponding buttons if you want that sky exposures are taken before and after the science exposures, or if you want that the reduction pipeline automatically computes the S-Index. In this last case you need to give the right value of the Vsin I in the first section of this form. Take into account that at this moment, the reduction pipeline and the roboter software do not consider the option of ThAr exposures just before and after the science exposure, but it may be implemented soon.

Additional comments

Please write here any important issue about the target.

List of spectra

A list of taken spectra is shown when you make a search on the archive, or when you click on the "listAllSpec" or "list Spec" button in the page of the proposal. These two buttons are only activated when the TIGRE has taken observations for the proposal or the object respectively.

If you click on the name of the PI of one of the observations, you can send an e-mail to the PI of the project.

To retrieve the spectra, select from the list those you want and at the end of the page choose which kind of data you require (raw only, raw+calib, reduced or all). Then, click on "Get". When the data are ready to be retrieved (typically a few seconds later if you don't require too many observations), you receive an e-mail with the instructions to download the data.

Notes

1. The PI of a project is the one that writes (and the only one that can edit) a proposal. A CoI can only retrieve the data.
2. The Archive system uses the e-mail addresses for the identification of the users. This is how the system identifies whether you work in one of the partners universities and how it links the CoI of your proposal with the users of the Archive. So be careful when yor write the e-mail address of you and your Co-I
3. THE EXPOSURE TIME CORRECTION FOR THE TIGRE
   To avoid underexposed spectra, we have implemented the exposure time correction for the TIGRE. In the case of bad observing conditions (clouds, bad seeing) the system can extend the exposure time to reach the desired S/N. It is to be noted that the output of the spectrograph is rather sensitive to the seeing conditions. This is because our fiber entrance has a diameter on the sky of 3". From theoretical and empirical calculation we have determined that if the seeing is 2", only 60% of the light of the star goes into the fiber and if the seeing is 3", the percentage of the light of a point source that feeds the fiber is <40%.
   When the astronomer request for it, the TIGRE can make a correction of the exposure time to adapt it to the current observing conditions.
   The exposure time correction is done in three steps. However, the first one is not yet implemented because some photometric nights are needed to make the necessary calibrations. These steps are:
   a) The Scheduler considers the past observing conditions during the night to select the next target to be observed.
   b) After the target has been acquired, the exposure time will be computed using the instrumental magnitude of the star, the seeing (both calculated by the acquisition and guiding unit) and the color B-V of the star.
   c) After each spectrum is obtained, it is calculated how good it is exposed (see below). This will be used to decide if a new exposure is needed to reach the requested S/N.
   The information required for the exposure time correction is the following:
   
   • From the astronomer: the magnitude V and the color B-V of the target, the requested minimum S/N of the resulting spectrum, and the suggested number of exposures (n) and exposure time of the individual exposures (texp). This suggested n and texp would be the values, that you have given in the proposal (using the exposure time calculator for normal conditions). In any case, this suggestion is a minimum: at least n exposures of texp sec. will be taken, regardless of how the observing conditions are. Also, if you ask for n>1 for the resulting spectrum, at least this number of exposures will be obtained (but if the reached S/N is not enough, more exposures may be taken).
     Depending on the total suggested exposure time (totSugExp=n*texp) a maximum total exposure time (maxTotExp) is calculated, being
     maxTotExp = 10* totSugExp for short suggested total exposure time and
     maxTotExp = 1.2 * totSugExp for observations requiring very long exposures.
     If in any of the three steps (see above) the calculated total exposure time that is necessary to reach the minimum S/N exceeds the maximum total exposure time, this observation will not be obtained / will be canceled. In this way we avoid to observe faint targets or objects that require very long exposure if the observing conditions are adverse and this time can be used for brighter objects.
   • From the acquisition image: the instrumental magnitude and the FWHM (seeing) of the star at the start of the autoguiding process. We have obtained an empirical relation between the output in the spectrograph and the instrumental magnitude, seeing and B-V of the star.
   • Finally, for each exposure (in both channels) it is calculated the average of the central part of a certain order (covering around 40% of the order). The relation between this value and the average S/N of the spectrum and the S/N at different wavelengths has been empirical determined, using the color B-V of the star.