Title  Chemical fractionation in Low-mass Cores
Pi     Y. Aikawa
Time   358 hrs

1. Name of program and authors
Name: Chemical fractionation in Low-mass Cores
     Authors: Y. Aikawa, K. Tatematsu

2. One short paragraph with science goal(s) From recent observational
studies, it became clear that the molecular abundances have local
spatial variation within molecular cloud cores. In the central region
of some prestellar cores C-bearing species (e.g. CO) are depleted,
while molecular D/H ratio is significantly enhanced and depletion of
N-bearing species are rare. Such fractionation is mainly caused by
molecular depletion onto grains and subsequent gas-phase
reactions. Detailed observation of the chemical fractionation reveals
not only the gas-dust chemical interaction, but also helps us to
understand the formation process of dense cores and their evolution,
because spatial abundance variation is determined by a balance between
physical and chemical timescales.

Molecules to be observed are CO, N2H+, H2D+, etc. Our source list
includes very young prestellar cores with little depletion, prestellar
cores with significant depletion, and very young protostellar cores,
which are not yet warm enough to start the hot-core type chemistry. We
need imaging of the dust continuum emission for reference. We will
observe two frequencies to disentangle the column density distribution
and the dust temperature distribution.


3. Number of sources: 3 starless cores and 3 protostellar cores

4. Coordinates:
4.1. Rough RA and DEC 
6 sources either in Lupus      (RA=15,    DEC=-40)
              or in Chamaeleon (RA=10:30, DEC=-78)
              or in Oph        (RA=16:30, DEC=-24)
              or in Taurus     (RA=04,    DEC=+20))

4.2. Moving target: no

4.3. Time critical: no

4.4. Scheduling constraints: (optional)

5. Spatial scales: 1. Angular resolution (arcsec): 2'' (For continuum,
5.we do not need 2" for comparison, but it would be better to observe
5.continuum at the same time slot, which means the same array
5.configuration. Otherwise, we must wait for array
5.re-configuration...)

5.2. Range of spatial scales/FOV (arcsec): 0.5'-2'
Band 3: 2'   - 9 field mosaic of FOV=50"
Band 4: 2'   - 25 field mosaic of FOV=33''
Band 6: 2'   - 36 field mosaic of FOV=20''
Band 7: 0.5' - 5 field mosaic of FOV=17''
Band 9: 0.5' - 25 field mosaic of FOV=8''

5.3. Required pointing accuracy: 0.1''

6. Observational setup
6.1. Single dish total power data: required
Observing modes for single dish total power: position switch

6.2. Stand-alone ACA: required

6.3. Cross-correlation of 7m ACA and 12m baseline-ALMA antennas: beneficial

6.4. Subarrays of 12m baseline-ALMA antennas: no


7. Frequencies:
7.1. Receiver band: Band 3, 4, 5, 6, 7, 8, or 9: 3, 4, 7, 9 (Band 6 for continuum ?)

7.2. Lines and Frequencies (GHz): 
Band 3 (3LO settings)
(1) H13CO+ (1-0): 87GHz
(2) N2H+ (1-0): 93GHz, C34S (2-1): 96GHz
(3) C18O (1-0): 110GHz, C17O(1-0): 112GHz
Band 4 (2LO settings): 
(1) DCO+ (2-1): 144GHz, DCN: 145GHz, C34S 2-1: 145GHz, CS(3-2): 147GHz
(2) N2D+ (2-1): 154GHz
Band 7 (1LO setting)
(1) H2D+: 372GHz
Band 9 (1LO setting)
(1) HD2+: 692GHz

7.3. Spectral resolution (km/s): 0.2 km/s

7.4. Bandwidth or spectral coverage (km/s or GHz): 5km/s

8. Continuum flux density:
8.1. Typical value (Jy): 20-400 mJ/beam at B6, 0.5-10J/beam at B9

8.2. Required continuum rms (Jy or K): 4 mJ/beam at B6, 28mJ/beam at B9

8.3. Dynamic range within image: 100

8.4. Calibration requirements: absolute      10%
                             repeatability  5%
                             relative       5%

9. Line intensity:
9.1. Typical value (K or Jy): 0.5-5 K

9.2. Required rms per channel (K or Jy): 0.07 K

9.3. Spectral dynamic range: 7-70

9.4. Calibration requirements: absolute      10%
                             repeatability  5%
                             relative       5%

10. Polarization: no
10.1. Required Stokes parameters:
10.2. Total polarized flux density (Jy):
10.3. Required polarization rms and/or dynamic range:
10.4. Polarization fidelity:
10.5. Required calibration accuracy:

11. Integration time for each observing mode/receiver setting (hr):
  6 sources x 9-field mosaic x 3 LO setting x 25 min =67.5 hrs (B3 line)
  6 sources x 25-field mosaic x 2 LO setting x 15 min =75 hrs (B4 line)
  3 sources x 5-field mosaic x 1LO setting x 120min =30 hrs (B7 line)
  3 sources x 25-field mosaic x 1LOsetting x 120min=150 hrs (B9 line)
  6 sources x 36-field mosaic x 1 min =3.6 hrs (B6 continuum)
6 sources x 320-field mosaic x 1 min = 32 hrs (B9 continuum)

12. Total integration time for program (hr): 358 hrs

13. Comments on observing strategy : (optional) We assume mosaic with
1-min imaging for continuum (The time will be reduced if OTF systhesis
is available in 2012).  OTF synthesis is preferable, because it will
improve UV coverage drastically and it will save observing time
largely.